World War I involved more countries and caused greater destruction than any other war except World War II (1939-1945). An assassin's bullets set off the war, and a system of military alliances plunged the main European powers into the fight. Each side expected quick victory but the war lasted four years and took the lives of nearly 10 million troops.

Several developments led to the awful bloodshed of the Great War, as World War I was originally called. War plants kept turning out vast quantities of newly invented weapons capable of extraordinary slaughter. Military drafts raised larger armies than ever before, and extreme patriotism gave many men a cause they were willing to die for. Propaganda whipped up support for the war by making the enemy seem villainous.

On June 28, 1914, an assassin gunned down Archduke Francis Ferdinand of Austria-Hungary in Sarajevo, the capital of Austria-Hungary's province of Bosnia-Herzegovina. The killer, Gavrilo Princip, had ties to a terrorist organization in Serbia, later part of Yugoslavia. Austria-Hungary believed that Serbia's government was behind the assassination and seized the opportunity to declare war on Serbia and settle an old feud.

The assassination of Francis Ferdinand sparked the outbreak of World War I but historians believe that the war had deeper causes. It resulted chiefly from the growth of extreme national pride among various European peoples, an enormous increase in European armed forces, a race for colonies, and the formation of military alliances. When the fighting began, France, Britain, and Russia -- who were known as the Allies -- backed Serbia. They opposed the Central Powers, made up of Austria-Hungary and Germany. Other nations later joined the Allies or the Central Powers.

Germany won early victories in World War I on the main European battlefronts. On the Western Front, France and Britain halted the German advance in September 1914. The opposing armies then fought from trenches that stretched across Belgium and northeastern France. The Western Front hardly moved for 3½ years in spite of fierce combat. On the Eastern Front, Russia battled Germany and Austria-Hungary. The fighting seesawed back and forth until 1917, when a revolution broke out in Russia and Russia soon asked for a truce.

The United States remained neutral at first but many Americans turned against the Central Powers after German submarines began sinking unarmed American ships. In 1917, the United States joined the Allies. U.S troops gave the Allies the manpower they needed to win the war. In the fall of 1918, the Central Powers surrendered.

World War I had results that none of the warring nations had foreseen. The war helped topple emperors in Austria-Hungary, Germany, and Russia. The peace treaties after the war carved new nations out of the defeated powers. The war left Europe exhausted, never to regain the controlling position in world affairs that it had held before the war. The peace settlement also created conditions that helped lead to World War II.

Causes of the war

The assassination of Archduke Francis Ferdinand triggered World War I. But the war had its origins in developments of the 1800's. The chief causes of World War I were (1) the rise of nationalism, (2) a build-up of military might, (3) competition for colonies, and (4) a system of military alliances.

The rise of nationalism. Europe avoided major wars in the 100 years before World War I began. Although small wars broke out, they did not involve many countries. But during the 1800's, a force swept across the continent that helped bring about the Great War. The force was nationalism -- the belief that loyalty to a person's nation and its political and economic goals comes before any other public loyalty. That exaggerated form of patriotism increased the possibility of war because a nation's goals inevitably came into conflict with the goals of one or more other nations. In addition, nationalistic pride caused nations to magnify small disputes into major issues. A minor complaint could thus quickly lead to the threat of war.

During the 1800's, nationalism took hold among people who shared a common language, history, or culture. Such people began to view themselves as members of a national group, or nation. Nationalism led to the creation of two new powers -- Italy and Germany -- through the uniting of many small states. War had a major role in achieving national unification in Italy and Germany.

Nationalist policies gained enthusiastic support as many countries in Western Europe granted the vote to more people. The right to vote gave citizens greater interest and greater pride in national goals. As a result, parliamentary governments grew increasingly powerful.

On the other hand, nationalism weakened the eastern European empires of Austria-Hungary, Russia, and Ottoman Turkey. Those empires ruled many national groups that clamored for independence. Conflicts among national groups were especially explosive in the Balkans -- the states on the Balkan Peninsula in southeastern Europe. The peninsula was known as the Powder Keg of Europe because tensions there threatened to ignite a major war. Most of the Balkans had been part of the Ottoman Empire. First Greece and then Montenegro, Serbia, Romania, Bulgaria, and Albania won independence in the period from 1821 to 1913. Each state quarreled with neighbors over boundaries. Austria-Hungary and Russia also took advantage of the Ottoman Empire's weakness to increase their influence in the Balkans.

Rivalry for control of the Balkans added to the tensions that erupted into World War I. Serbia led a movement to unite the region's Slavs. Russia, the most powerful Slavic country, supported Serbia. But Austria-Hungary feared Slavic nationalism, which stirred unrest in its empire. Millions of Slavs lived under Austria-Hungary's rule. In 1908, Austria-Hungary greatly angered Serbia by adding the Balkan territory of Bosnia-Herzegovina to its empire. Serbia wanted control of this area because many Serbs lived there.

A build-up of military might occurred among European countries before World War I broke out. Nationalism encouraged public support for military build-ups and for a country's use of force to achieve its goals. By the late 1800's, Germany had the best-trained army in the world. It relied on a military draft of all able-bodied young men to increase the size and strength of its peacetime army. Other European countries followed Germany's lead and expanded their standing armies.

At first, Britain remained unconcerned about Germany's military build-up. Britain, an island country, relied on its navy for defense -- and it had the world's strongest navy. But in 1898, Germany began to develop a naval force big enough to challenge the British navy. Germany's decision to become a major seapower made it a bitter enemy of Great Britain. In 1906, the British navy launched the Dreadnought, the first modern battleship. The heavily armed Dreadnought had greater firepower than any other ship of its time. Germany rushed to construct ships like it.

Advances in technology -- the tools, materials, and techniques of industrialization -- increased the destructive power of military forces. Machine guns and other new arms fired more accurately and more rapidly than earlier weapons. Steamships and railroads could speed the movement of troops and supplies. By the end of the 1800's, technology enabled countries to fight longer wars and bear greater losses than ever before, yet military experts insisted that future wars would be short.

Competition for colonies. During the late 1800's and early 1900's, European nations carved nearly all of Africa and much of Asia into colonies. The race for colonies was fueled by Europe's increasing industrialization. Colonies supplied European nations with raw materials for factories, markets for manufactured goods, and opportunities for investment. But the competition for colonies strained relations among European countries. Incidents between rival powers flared up almost every year. Several of the clashes nearly led to war.

A system of military alliances gave European powers a sense of security before World War I. A country hoped to discourage an attack from its enemies by entering into a military agreement with one or more other countries. In case of an attack, such an agreement guaranteed that other members of the alliance would come to the country's aid or at least remain neutral.

Although military alliances provided protection for a country, the system created certain dangers. Because of its alliances, a country might take risks in dealings with other nations that it would hesitate to take alone. If war came, the alliance system meant that a number of nations would fight, not only the two involved in a dispute. Alliances could force a country to go to war against a nation it had no quarrel with or over an issue it had no interest in. In addition, the terms of many alliances were kept secret. The secrecy increased the chances that a country might guess wrong about the consequences of its actions.

The Triple Alliance. Germany was at the center of European foreign policy from 1870 until the outbreak of World War I. Chancellor Otto von Bismarck, Germany's prime minister, formed a series of alliances to strengthen his country's security. He first made an ally of Austria-Hungary. In 1879, Germany and Austria-Hungary agreed to go to war if either country were attacked by Russia. Italy joined the agreement in 1882, and it became known as the Triple Alliance. The members of the Triple Alliance agreed to aid one another in the case of an attack by two or more countries.

Bismarck also brought Austria-Hungary and Germany into an alliance with Russia. The agreement, known as the Three Emperors' League, was formed in 1881. The three powers agreed to remain neutral if any of them went to war with another country. Bismarck also persuaded Austria-Hungary and Russia, which were rivals for influence in the Balkans, to recognize each other's zone of authority in the region. He thus reduced the danger of conflict between the two countries.

Germany's relations with other European countries worsened after Bismarck left office in 1890. Bismarck had worked to prevent France, Germany's neighbor on the west, from forming an alliance with either of Germany's two neighbors to the east -- Russia and Austria-Hungary. In 1894, France and Russia agreed to mobilize (call up troops) if any nation in the Triple Alliance mobilized. France and Russia also agreed to help each other if either were attacked by Germany.

The Triple Entente. During the 1800's, Britain had followed a foreign policy that became known as "splendid isolation." But Germany's naval build-up made Britain feel the need for allies. The country therefore ended its isolation. In 1904, Britain and France settled their past disagreements over colonies and signed the Entente Cordiale (Friendly Agreement). Although the agreement contained no pledges of military support, the two countries began to discuss joint military plans. In 1907, Russia joined the Entente Cordiale, and it became known as the Triple Entente.

The Triple Entente did not obligate its members to go to war as the Triple Alliance did. But the alliances left Europe divided into two opposing camps.

Beginning of the war

World War I began in the Balkans, the site of many small wars. In the early 1900's, the Balkan states fought the Ottoman Empire in the First Balkan War (1912-1913) and one another in the Second Balkan War (1913). The major European powers stayed out of both wars. But they did not escape the third Balkan crisis.

The assassination of an archduke. Archduke Francis Ferdinand, heir to the throne of Austria-Hungary, hoped that his sympathy for Slavs would ease tensions between Austria-Hungary and the Balkans. He arranged to tour Bosnia-Herzegovina with his wife, Sophie. As the couple rode through Sarajevo on June 28, 1914, an assassin jumped on their automobile and fired two shots. Francis Ferdinand and Sophie died almost instantly. The murderer, Gavrilo Princip, was linked to a Serbian terrorist group called the Black Hand.

The assassination of Francis Ferdinand gave Austria-Hungary an excuse to crush Serbia, its long-time enemy in the Balkans. Austria-Hungary first gained Germany's promise of support for any action it took against Serbia. It then sent a list of humiliating demands to Serbia on July 23. Serbia accepted most of the demands and offered to have the rest settled by an international conference. Austria-Hungary rejected the offer and declared war on Serbia on July 28. It expected a quick victory.

How the conflict spread. Within weeks of the archduke's assassination, the chief European powers were drawn into World War I. A few attempts were made to prevent the war. For example, Britain proposed an international conference to end the crisis. But Germany rejected the idea, claiming that the dispute involved only Austria-Hungary and Serbia. However, Germany tried to stop the war from spreading. The German kaiser (emperor), Wilhelm II, urged Czar Nicholas II of Russia, his cousin, not to mobilize.

Russia had backed down before in supporting its Serbian ally. In 1908, Austria-Hungary had angered Serbia by taking over Bosnia-Herzegovina, and Russia had stepped aside. In 1914, Russia vowed to stand behind Serbia. Russia first gained a promise of support from France. The czar then approved plans to mobilize along Russia's border with Austria-Hungary. But Russia's military leaders persuaded the czar to mobilize along the German border, too. On July 30, 1914, Russia announced it would mobilize fully.

Germany declared war on Russia on Aug. 1, 1914, in response to Russia's mobilization. Two days later, Germany declared war on France. The German army swept into Belgium on its way to France. The invasion of neutral Belgium caused Britain to declare war on Germany on August 4. By the time the war ended in November 1918, few areas of the world had remained neutral.

The Western Front. Germany's war plan had been prepared in 1905 by Alfred von Schlieffen. Schlieffen was chief of the German General Staff, the group of officers who provided advice on military operations. The Schlieffen Plan assumed that Germany would have to fight both France and Russia. It aimed at a quick defeat of France while Russia slowly mobilized. After defeating France, Germany would deal with Russia. The Schlieffen Plan required Germany to strike first if war came. Once the plan was set in motion, the system of military alliances almost assured a general European war.

The Schlieffen Plan called for two wings of the German army to crush the French army in a pincers movement. A small left wing would defend Germany along its frontier with France. A much larger right wing would invade France through Belgium; encircle and capture France's capital, Paris; and then move east. As the right wing moved in, the French forces would be trapped between the pincers. The success of Germany's assault depended on a strong right wing. However, Helmuth von Moltke, who had become chief of the General Staff in 1906, directed German strategy at the outbreak of World War I. Moltke changed the Schlieffen Plan by reducing the number of troops in the right wing.

Belgium's army fought bravely but held up the Germans for only a short time. By Aug. 16, 1914, the right wing of the German army could begin its pincers motion. It drove back French forces and a small British force in southern Belgium and swept into France. But instead of swinging west around Paris according to plan, one part of the right wing pursued retreating French troops east toward the Marne River. This maneuver left the Germans exposed to attacks from the rear.

Meanwhile, General Joseph Joffre, commander in chief of all the French armies, stationed his forces near the Marne River east of Paris and prepared for battle. Fierce fighting, which became known as the First Battle of the Marne, began on September 6. On September 9, German forces started to withdraw.

The First Battle of the Marne was a key victory for the Allies because it ended Germany's hopes to defeat France quickly. Moltke was replaced as chief of the German General Staff by Erich von Falkenhayn.

The German army halted its retreat near the Aisne River. From there, the Germans and the Allies fought a series of battles that became known as the Race to the Sea. Germany sought to seize ports on the English Channel and cut off vital supply lines between France and Britain. But the Allies stopped the German advance to the sea in the First Battle of Ypres in Belgium. The battle lasted from mid-October until mid-November.

By late November 1914, the war reached a deadlock along the Western Front as neither side gained much ground. The battlefront extended more than 450 miles across Belgium and northeastern France to the border of Switzerland. The deadlock on the Western Front lasted nearly 3½ years.

The Eastern Front. Russia's mobilization on the Eastern Front moved faster than Germany expected. By late August 1914, two Russian armies had thrust deeply into the German territory of East Prussia. The Germans learned that the two armies had become separated, and they prepared a battle plan. By August 31, the Germans had encircled one Russian army in the Battle of Tannenberg. They then chased the other Russian army out of East Prussia in the Battle of the Masurian Lakes. The number of Russian casualties -- that is, the number of men killed, captured, wounded, or missing -- totaled about 250,000 in the two battles. The victories made heroes of the commanders of the German forces in the east -- Paul von Hindenburg and Erich Ludendorff.

Austria-Hungary had less success than its German ally on the Eastern Front. By the end of 1914, Austria-Hungary's forces had attacked Serbia three times and been beaten back each time. Meanwhile, Russia had captured much of the Austro-Hungarian province of Galicia (now part of Poland and Ukraine). By early October, a humiliated Austro-Hungarian army had retreated into its own territory.

Fighting elsewhere. The Allies declared war on the Ottoman Empire in November 1914, after Turkish ships bombarded Russian ports on the Black Sea. Turkish troops then invaded Russia. Fighting later broke out in the Ottoman territories on the Arabian Peninsula and in Mesopotamia (now mostly Iraq), Palestine, and Syria.

Britain stayed in control of the seas following two naval victories over Germany in 1914. The British then kept Germany's surface fleet bottled up in its home waters during most of the war. As a result, Germany relied on submarine warfare.

World War I quickly spread to Germany's overseas colonies. Japan declared war on Germany in late August 1914 and drove the Germans off several islands in the Pacific Ocean. Troops from Australia and New Zealand seized other German colonies in the Pacific. By mid-1915, most of Germany's empire in Africa had fallen to British forces. However, fighting continued in German East Africa (now Tanzania) for two more years.

The deadlock on the Western Front

By 1915, the opposing sides had dug themselves into a system of trenches that zigzagged along the Western Front. From the trenches, they defended their positions and launched attacks. The Western Front remained deadlocked in trench warfare until 1918.

Trench warfare. The typical front-line trench was about 6 to 8 feet deep and wide enough for two men to pass. Dugouts in the sides of the trenches protected men during enemy fire. Support trenches ran behind the front-line trenches. Off-duty soldiers lived in dugouts in the support trenches. Troops and supplies moved to the battlefront through a network of communications trenches. Barbed wire helped protect the front-line trenches from surprise attacks. Field artillery was set up behind the support trenches. Between the enemy lines lay a stretch of ground called "no man's land." No man's land varied from less than 30 yards wide at some points to more than 1 mile wide at others. In time, artillery fire tore up the earth, making it very difficult to cross no man's land during an attack.

Soldiers generally served at the front line from a few days to a week and then rotated to the rear for a rest. Life in the trenches was miserable. The smell of dead bodies lingered in the air, and rats were a constant problem. Soldiers had trouble keeping dry, especially in water-logged areas of Belgium. Except during an attack, life fell into a dull routine. Some soldiers stood guard. Others repaired the trenches, kept telephone lines in order, brought food from behind the battle lines, or did other jobs. At night, patrols fixed the barbed wire and tried to get information about the enemy.

Enemy artillery and machine guns kept each side pinned in the trenches. Yet the Allies repeatedly tried to blast a gap in the German lines. Allied offensives (assaults) followed a pattern. First, artillery bombarded the enemy front-line trenches. The infantry then attacked as commanders shouted, "Over the top!" Soldiers scrambled out of trenches and began the dash across no man's land with fixed bayonets. They hurled grenades into enemy trenches and struggled through the barbed wire. But the artillery bombardment seldom wiped out all resistance, and so enemy machine guns slaughtered wave after wave of advancing infantry. Even if the attackers broke through the front line, they ran into a second line of defenses. Thus, the Allies never cracked the enemy's defensive power.

Both the Allies and the Central Powers developed new weapons, which they hoped would break the deadlock. In April 1915, the Germans first released poison gas over Allied lines in the Second Battle of Ypres. The fumes caused vomiting and suffocation. But German commanders had little faith in the gas, and they failed to seize that opportunity to launch a major attack. The Allies also began to use poison gas soon thereafter, and gas masks became necessary equipment in the trenches. Another new weapon was the flame thrower, which shot out a stream of burning fuel.

The Battle of Verdun. As chief of the German General Staff, Falkenhayn decided in early 1916 to concentrate on killing enemy soldiers. He hoped that the Allies would finally lack the troops to continue the war. Falkenhayn chose to attack the French city of Verdun. He believed that France would defend Verdun to the last man. Fierce bombardment began on February 21.

Joffre, commander of the French armies, felt that the loss of Verdun would severely damage French morale. Through spring and summer, the French forces held off the attackers. As Falkenhayn predicted, France kept pouring men into the battle. However, Falkenhayn had not expected the battle to take nearly as many German lives as French lives. He halted the unsuccessful assault in July 1916. The next month, Hindenburg and Ludendorff -- the two German heroes of the Eastern Front -- replaced Falkenhayn on the Western Front. Hindenburg became chief of the General Staff. Ludendorff, his top aide, planned German strategy.

General Henri Petain had organized the defense of Verdun and was hailed a hero by France. The Battle of Verdun became a symbol of the terrible destructiveness of modern war. French casualties totaled about 315,000 men, and German casualties about 280,000. The city itself was practically destroyed.

The Battle of the Somme. The Allies planned a major offensive for 1916 near the Somme River in France. The Battle of Verdun had drained France. Thus, the Somme offensive became mainly the responsibility of the British under General Douglas Haig.

The Allies attacked on July 1, 1916. Within hours, Britain had suffered nearly 60,000 casualties -- its worst loss in one day of battle. Fierce fighting went on into the fall. In September, Britain introduced the first primitive tanks. But the tanks were too unreliable and too few in number to make a difference in the battle. Haig finally halted the useless attack in November. At terrible cost, the Allies had gained about 7 miles. The Battle of the Somme caused more than 1 million casualties -- over 600,000 Germans, over 400,000 British, and nearly 200,000 French. In spite of the tragic losses at Verdun and the Somme, the Western Front stood as solid as ever at the end of 1916.

The war on other fronts

During 1915 and 1916, World War I spread to Italy and throughout the Balkans, and activity increased on other fronts. Some Allied military leaders believed that the creation of new battlefronts would break the deadlock on the Western Front. But the war's expansion had little effect on the deadlock.

The Italian Front. Italy had stayed out of World War I during 1914, even though it was a member of the Triple Alliance with Austria-Hungary and Germany. Italy claimed that it was under no obligation to honor the agreement because Austria-Hungary had not gone to war in self-defense. In May 1915, Italy entered World War I on the side of the Allies. In a secret treaty, the Allies promised to give Italy some of Austria-Hungary's territory after the war. In return, Italy promised to attack Austria-Hungary.

The Italians, led by General Luigi Cadorna, hammered away at Austria-Hungary for two years in a series of battles along the Isonzo River in Austria-Hungary. Italy suffered enormous casualties but gained very little territory. The Allies hoped that the Italian Front would help Russia by forcing Austria-Hungary to shift some troops away from the Eastern Front. Such a shift occurred, but it did not help Russia.

The Dardanelles. After World War I began, the Ottoman Empire closed the waterway between the Aegean Sea and the Black Sea. It thereby blocked the sea route to southern Russia. French and British warships attacked the Dardanelles, a strait that formed part of the waterway, in February and March 1915. The Allies hoped to open a supply route to Russia. However, underwater mines halted the assault.

In April 1915, the Allies landed troops on the Gallipoli Peninsula on the west shore of the Dardanelles. Troops from Australia and New Zealand played a key role in the landing. Ottoman and Allied forces soon became locked in trench warfare. A second invasion in August at Suvla Bay to the north failed to end the standstill. In December, the Allies began to evacuate their troops. They had suffered about 250,000 casualties in the Dardanelles.

Eastern Europe. In May 1915, the armies of Germany and Austria-Hungary broke through Russian lines in Galicia, the Austro-Hungarian province that Russia had invaded in 1914. The Russians retreated about 300 miles before they formed a new line of defense. In spite of the setback, Czar Nicholas II staged two offensives to relieve the pressure on the Allies on the Western Front. The first Russian offensive, in March 1916, failed to pull German troops away from Verdun.

The second Russian offensive began in June 1916 under General Alexei Brusilov. Brusilov's army drove Austria-Hungary's forces back about 50 miles. Within a few weeks, Russia captured about 200,000 prisoners. To halt the assault, Austria-Hungary had to shift troops from the Italian Front to the Eastern Front. The Russian offensive nearly knocked Austria-Hungary out of the war. But it also exhausted Russia. Each side suffered about a million casualties.

Bulgaria entered World War I in October 1915 to help Austria-Hungary defeat Serbia. Bulgaria hoped to recover land it had lost in the Second Balkan War. In an effort to aid Serbia, the Allies landed troops in Thessaloniki (Salonika), Greece. But the troops never reached Serbia. By November, the Central Powers had overrun Serbia, and Serbia's army had retreated to Albania.

Romania joined the Allies in August 1916. It hoped to gain some of Austria-Hungary's territory if the Allies won the war. By the end of 1916, Romania had lost most of its army, and Germany controlled the country's valuable wheat fields and oil fields.

The war at sea. Great Britain's control of the seas during World War I caused serious problems for Germany. The British navy blockaded German waters, preventing supplies from reaching German ports. By 1916, Germany suffered a shortage of food and other goods. Germany combated British seapower with its submarines, called U-boats. In February 1915, Germany declared a submarine blockade of the British Isles and warned that it would attack any ship that tried to get through the blockade. Thereafter, U-boats destroyed great amounts of goods headed for Britain.

On May 7, 1915, a U-boat torpedoed without warning the British passenger liner Lusitania off the coast of Ireland. Among the 1,198 passengers who died 128 were Americans. The sinking of the Lusitania led U.S. President Woodrow Wilson to urge Germany to give up unrestricted submarine warfare. In September, Germany agreed not to attack neutral or passenger ships.

The warships that Britain and Germany had raced to build before World War I remained in home waters during most of the war. There, they served to discourage an enemy invasion. The only major encounter between the two navies was the Battle of Jutland. It was fought off the coast of Denmark on May 31 and June 1, 1916. Admiral Sir John Jellicoe commanded a British fleet of 150 warships. He faced a German fleet of 99 warships under the command of Admiral Reinhard Scheer. In spite of Britain's superior strength, Jellicoe acted cautiously. He feared that he could lose the entire war in a day because the destruction of Britain's fleet would give Germany control of the seas. Both sides claimed victory in the Battle of Jutland. Although Britain lost more ships than Germany, it still ruled the seas.

The war in the air. Great advances in aviation were made by the Allies and the Central Powers during World War I. Each side competed to produce better airplanes than the other side. Airplanes were used mainly to observe enemy activities. The pilots carried guns to shoot down enemy planes. But a pilot risked shooting himself if a bullet bounced off the propeller.

In 1915, Germany developed a machine gun timed to fire between an airplane's revolving propeller blades. The invention made air combat more deadly and led to dogfights -- clashes between enemy aircraft. A pilot who shot down 5 or more enemy planes was called an ace. Many aces became national heroes. Germany's Baron Manfred von Richthofen, who was known as the Red Baron, shot down 80 planes, more than any other ace. Other famous aces included Billy Bishop of Canada, Rene Fonck of France, Edward Mannock of Great Britain, and Eddie Rickenbacker of the United States.

Aerial bombing remained in its early stages during World War I. In 1915, Germany began to bomb London and other British cities from airships called zeppelins. But bombing had little effect on the war.

The final stage

Allied failures. During 1917, French and British military leaders still hoped that a successful offensive could win the war. But German leaders accepted the deadlock on the Western Front and improved German defenses. In March 1917, German troops were moved back to a strongly fortified new battle line in northern France. It was called the Siegfried Line by the Germans and the Hindenburg Line by the Allies. The Siegfried Line shortened the Western Front and placed German artillery and machine guns to best advantage. It also led to the failure of an offensive planned by France.

General Robert Nivelle had replaced Joffre as commander in chief of French forces in December 1916. Nivelle planned a major offensive near the Aisne River and predicted he would smash through the German line within two days. Nivelle's enthusiasm inspired the French troops. Germany's pullback to the Siegfried Line did not shake Nivelle's confidence.

In April 1917, shortly before Nivelle's offensive began, Canadian forces seized a hill called Vimy Ridge. Many Allied troops had fallen in earlier attempts to dislodge the Germans from that height in northern France.

Nivelle's offensive opened on April 16, 1917. By the end of the day, it was clear that the assault had failed. But fighting continued into May. Mutinies broke out among the French forces after Nivelle's offensive collapsed. The troops had had enough of the pointless bloodshed and the horrid conditions on the Western Front. They no longer had faith in their leaders. Men who had fought bravely for almost three years refused to go on fighting. Petain, the hero of Verdun, replaced Nivelle in May 1917. Petain improved the soldiers' living conditions and restored order. He promised that France would remain on the defensive until it was ready to fight again. Meanwhile, any further offensives on the Western Front remained Britain's responsibility.

General Haig was hopeful that a British offensive near Ypres would lead to victory. The Third Battle of Ypres, also known as the Battle of Passchendaele, began on July 31, 1917. For more than three months, British troops and a small French force pounded the Germans in an especially terrible campaign. Heavy Allied bombardment before the infantry attack began had destroyed the drainage system around Ypres. Drenching rains then turned the water-logged land into a swamp where thousands of British soldiers drowned. Snow and ice finally halted the disastrous battle on November 10. In late November, Britain used tanks to break through the Siegfried Line. But the failure at Ypres had used up the troops Britain needed to follow up that success.

In 1917, first France and then Britain thus saw their hopes for victory shattered. Austria-Hungary drove the Italians out of its territory in the Battle of Caporetto in the fall. A revolution in Russia made the Allied situation seem even more hopeless.

The Russian Revolution. The Russian people suffered greatly during World War I. By 1917, many of them were no longer willing to put up with the enormous casualties and the severe shortages of food and fuel. They blamed Czar Nicholas II and his advisers for the country's problems. Early in 1917, an uprising in Petrograd (now St. Petersburg) forced Nicholas from the throne. The new government continued the war.

To weaken Russia's war effort further, Germany helped V. I. Lenin, a Russian revolutionary then living in Switzerland, return to his homeland in April 1917. Seven months later, Lenin led an uprising that gained control of Russia's government. Lenin immediately called for peace talks with Germany. World War I had ended on the Eastern Front.

Germany dictated harsh peace terms to Russia in a peace treaty signed in Brest-Litovsk, Russia, on March 3, 1918. The Treaty of Brest-Litovsk forced Russia to give up large amounts of territory, including Finland, Poland, Ukraine, Bessarabia, and the Baltic States -- Estonia, Livonia (now Latvia), and Lithuania. The end of the fighting on the Eastern Front freed German troops for use on the Western Front. The only obstacle to a final German victory seemed to be the entry of the United States into the war.

The United States enters the war. At the start of World War I, President Wilson had declared the neutrality of the United States. Most Americans opposed U.S. involvement in a European war. But the sinking of the Lusitania and other German actions against civilians drew American sympathies to the Allies.

Several events early in 1917 persuaded the United States government to enter World War I. In February, Germany returned to unrestricted submarine warfare, which it assumed might bring the United States into the war. But German military leaders believed that they could still win the war by cutting off British supplies. They expected their U-boats to starve Britain into surrendering within a few months, long before the United States had fully prepared for war.

Tension between the United States and Germany increased after the British intercepted and decoded a message from Germany's foreign minister, Arthur Zimmermann, to the German ambassador to Mexico. The message, known as the "Zimmermann note," revealed a German plot to persuade Mexico to go to war against the United States. The British gave the message to Wilson, and it was published in the United States early in March. Americans were further enraged after U-boats sank several U.S. cargo ships.

On April 2, Wilson called for war, stating that "the world must be made safe for democracy." Congress declared war on Germany on April 6. Few people expected that the United States would make much of a contribution toward ending the war.

Mobilization. The United States entered World War I unprepared for battle. Strong antiwar feelings had hampered efforts to prepare for war. After declaring war, the government worked to stir up enthusiasm for the war effort. Government propaganda pictured the war as a battle for liberty and democracy. People who still opposed the war faced increasingly unfriendly public opinion. They could even be brought to trial under wartime laws forbidding statements that might harm the successful progress of the war.

During World War I, U.S. government agencies directed the nation's economy toward the war effort. President Wilson put financier Bernard M. Baruch in charge of the War Industries Board, which turned factories into producers of war materials. The Food Administration, headed by businessman Herbert Hoover, controlled the prices, production, and distribution of food. Americans observed "meatless" and "wheatless" days in order that food could be sent to Europe.

Manpower was the chief contribution of the United States to World War I. The country entered the war with a Regular Army of only about 128,000 men. It soon organized a draft requiring all men from 21 through 30 years old to register for military service. The age range was broadened to 18 through 45 in 1918. A lottery determined who served. Many men enlisted voluntarily, and women signed up as nurses and office workers. The U.S. armed forces had almost 5 million men and women by the end of the war. Of that number, about 23/4 million men had been drafted. Few soldiers received much training before going overseas because the Allies urgently needed them.

Before U.S. help could reach the Western Front, the Allies had to overcome the U-boat threat in the Atlantic. In May 1917, Britain began to use a convoy system, by which cargo ships went to sea in large groups escorted by warships. The U-boats proved no match for the warships, and Allied shipping losses dropped sharply.

American troops in Europe. The soldiers sent to Europe by the U.S. Army made up the American Expeditionary Forces (AEF). General John J. Pershing, commander of the AEF, arrived in France in mid-June 1917. The first troops landed later that month. Pershing told U.S. military authorities that he needed 3 million American troops, a third of them within the next year. The American officials were shocked. They had planned to send only 650,000 troops in that time. In the end, about 2 million Americans served in Europe.

Britain, France, and Italy knew well how desperately they needed U.S. manpower by the fall of 1917. In November, the Allies formed the Supreme War Council to plan strategy. They decided to make their strategy defensive until U.S. troops reached the Western Front. The Allies wanted Americans to serve as replacements and fill out their battered ranks. But Pershing was convinced that the AEF would make a greater contribution by fighting as an independent unit. The argument was the major wartime dispute between the Europeans and their American ally. Pershing generally held firm, though at times he lent troops to France and Britain.

The last campaigns. The end of the war on the Eastern Front boosted German hopes for victory. By early 1918, German forces outnumbered the Allies on the Western Front. In spring, Germany staged three offensives. Ludendorff counted on delivering a crushing blow to the Allies before large numbers of American troops reached the front. He relied on speed and surprise.

Germany first struck near St.-Quentin, a city in the Somme River Valley, on March 21, 1918. By March 26, British troops had retreated about 30 miles. In late March, the Germans began to bombard Paris with "Big Berthas." The enormous guns hurled shells up to 75 miles. After the disaster at St.-Quentin, Allied leaders met to plan a united defense. In April, they appointed General Ferdinand Foch of France to be the supreme commander of the Allied forces on the Western Front.

A second German offensive began on April 9 along the Lys River in Belgium. British troops fought stubbornly, and Ludendorff called off the attack on April 30. The Allies suffered heavy losses in both assaults, but German casualties were nearly as great.

Germany attacked a third time on May 27 near the Aisne River. By May 30, German troops had reached the Marne River. American soldiers helped France stop the German advance at the town of Chateau-Thierry, less than 50 miles northeast of Paris. During June, U.S. troops drove the Germans out of Belleau Wood, a forested area near the Marne. German forces crossed the Marne on July 15. Foch ordered a counterattack near the town of Soissons on July 18.

The Second Battle of the Marne was fought from July 15 through Aug. 6, 1918. It marked the turning point of World War I. After winning the battle, the Allies advanced steadily. On August 8, Britain and France attacked the Germans near Amiens. By early September, Germany had lost all the territory it had gained since spring. In mid-September, Pershing led U.S. forces to easy victory at St.-Mihiel.

The last offensive of World War I began on Sept. 26, 1918. About 900,000 U.S. troops participated in heavy fighting between the Argonne Forest and the Meuse River. Ludendorff realized that Germany could no longer overcome the superior strength of the Allies.

The fighting ends. The Allies won victories on all fronts in the fall of 1918. Bulgaria surrendered on September 29. British forces under the command of General Edmund Allenby triumphed over the Ottoman army in Palestine and Syria. On October 30, the Ottoman Empire signed an armistice. The last major battle between Italy and Austria-Hungary began in late October in Italy. Italy, with support from France and Great Britain, defeated Austria-Hungary near the town of Vittorio Veneto. Austria-Hungary signed an armistice on November 3.

Germany teetered on the edge of collapse as the war continued through October. Britain's naval blockade had nearly starved the German people, and widespread discontent led to riots and rising demands for peace. Kaiser Wilhelm gave up his throne on November 9 and fled to the Netherlands. An Allied delegation headed by Foch met with German representatives in a railroad car in the Compiegne Forest in northern France.

In the early morning on Nov. 11, 1918, the Germans accepted the armistice terms demanded by the Allies. Germany agreed to evacuate the terrorities it had taken during the war; to surrender large numbers of arms, ships, and other war materials; and to allow the Allied powers to occupy German territory along the Rhine River. Foch ordered the fighting to stop on the Western Front at 11 a.m. World War I was over.

Consequences of the war

Destruction and casualties. World War I caused immeasurable destruction. Nearly 10 million soldiers died as a result of the war -- far more than had died in all the wars during the previous 100 years. About 21 million men were wounded. The enormously high casualties resulted partly from the destructive powers of new weapons, especially the machine gun. Military leaders contributed to the slaughter by failing to adjust to the changed conditions of warfare. In staging offensives, they ordered soldiers armed with bayonets into machine-gun fire. Only in the last year of the war did generals successfully use tanks and new tactics.

Germany and Russia each suffered about 1¾ million battle deaths during World War I -- more than any other country. France had the highest percentage of battle deaths in relation to its total number of servicemen. It lost about 1¾ million soldiers, or 16 per cent of those mobilized. No one knows how many civilians died of disease, starvation, and other war-related causes. Some historians believe as many civilians died as soldiers.

Property damage in World War I was greatest in France and Belgium. Armies destroyed farms and villages as they passed through them or, even worse, dug in for battle. The fighting wrecked factories, bridges, and railroad tracks. Artillery shells, trenches, and chemicals made barren the land along the Western Front.

Economic consequences. World War I cost the fighting nations a total of about $337 billion dollars. By 1918, the war was costing about $10 million an hour. Nations raised part of the money to pay for the war through income taxes and other taxes. But most of the money came from borrowing, which created huge debts. Governments borrowed from citizens by selling war bonds. The Allies also borrowed heavily from the United States. In addition, most governments printed extra money to meet their needs. But the increased money supply caused severe inflation after the war.

The problem of war debts lingered after World War I ended. The Allies tried to reduce their debts by demanding reparations (payments for war damages) from the Central Powers, especially Germany. Reparations worsened the economic problems of the defeated countries and did not solve the problems of the victors.

World War I seriously disrupted economies. Some businesses shut down after workers left for military service. Other firms shifted to the production of war materials. To direct production toward the war effort, governments took greater control over the economy than ever before. Most people wanted a return to private enterprise after the war. But some people expected government to continue to solve economic problems.

The countries of Europe had poured their resources into World War I, and they came out of the war exhausted. France, for example, had lost nearly one-tenth of its work force. In most European countries, many returning soldiers could not find jobs. In addition, Europe lost many of the markets for its exports while producing war goods. The United States and other countries that had played a smaller role in the war emerged with increased economic power.

Political consequences. World War I shook the foundations of several governments. Democratic governments in Britain and France withstood the stress of the war. But four monarchies toppled. The first monarch to fall was Czar Nicholas II of Russia in 1917. Kaiser Wilhelm II of Germany and Emperor Charles of Austria-Hungary left their thrones in 1918. The Ottoman sultan, Muhammad VI, fell in 1922.

The collapse of old empires led to the creation of new countries in the years after World War I. The prewar territory of Austria-Hungary formed the independent republics of Austria, Hungary, and Czechoslovakia, as well as parts of Italy, Poland, Romania, and Yugoslavia. Russia and Germany also gave up territory to Poland. Finland and the Baltic States -- Estonia, Latvia, and Lithuania -- gained independence from Russia. Most Arab lands in the Ottoman Empire were placed under the control of France and Britain. The rest of the Ottoman Empire became Turkey. European leaders took national groups into account in redrawing the map of Europe and thus strengthened the cause of nationalism.

World War I gave the Communists a chance to seize power in Russia. Some people expected Communist revolutions to break out elsewhere in Europe. Revolutionary movements gained strength after the war, but Communist governments did not take hold.

Social consequences. World War I brought enormous changes in society. The death of so many young men affected France more than other countries. During the 1920's, France's population dropped because of a low birth rate. Millions of people were uprooted by the war. Some fled war-torn areas and later found their houses, farms, or villages destroyed. Others became refugees as a result of changes in governments and national borders, especially in central and eastern Europe.

Many people chose not to resume their old way of life after World War I. Urban areas grew as peasants settled in cities instead of returning to farms. Women filled jobs in offices and factories after men went to war, and they were reluctant to give up their new independence. Many countries granted women the vote after the war.

The distinction between social classes began to blur as a result of World War I, and society became more democratic. The upper classes, which had traditionally governed, lost some of their power and privilege after having led the world into an agonizing war. Men of all classes had faced the same danger and horror in the trenches. Those who had bled and suffered for their country came to demand a say in running it.

Finally, World War I transformed attitudes. Middle- and upper-class Europeans lost the confidence and optimism they had felt before the war. Many people began to question long-held ideas. For example, few Europeans before the war had doubted their right to force European culture on the rest of the world. But the destruction and bloodshed of the war shattered the belief in the superiority of European civilization.

The peace settlement

The Fourteen Points. In January 1918, 10 months before World War I ended, President Woodrow Wilson of the United States proposed a set of war aims called the Fourteen Points. Wilson believed that the Fourteen Points would bring about a just peace settlement, which he termed "peace without victory." In November 1918, Germany agreed to an armistice. Germany expected that the peace settlement would be based on the Fourteen Points.

Eight of Wilson's Fourteen Points dealt with specific political and territorial settlements. The rest of them set forth general principles aimed at preventing future wars. The last point proposed the establishment of an international association -- later called the League of Nations -- to maintain the peace.

The Paris Peace Conference. In January 1919, representatives of the victorious powers gathered in Paris to draw up the peace settlement. They came from 32 nations. Committees worked out specific proposals at the Paris Peace Conference. But the decisions were made by four heads of government called the Big Four. The Big Four consisted of Wilson, Britain's Prime Minister David Lloyd George, France's Premier Georges Clemenceau, and Italy's Premier Vittorio Orlando.

The Paris Peace Conference largely disregarded the lofty principles of the Fourteen Points. The major European Allies had sacrificed far more than the Americans and wanted to be paid back. Wilson focused his efforts on the creation of the League of Nations. He yielded to France and Britain on many other issues.

In May 1919, the peace conference approved the treaty and presented it to Germany. Germany agreed to it only after the Allies threatened to invade. With grave doubts, German representatives signed the treaty in the Palace of Versailles near Paris on June 28, 1919. The date was the fifth anniversary of the assassination of Archduke Francis Ferdinand.

In addition to the Treaty of Versailles with Germany, the peacemakers drew up separate treaties with the other Central Powers. The Treaty of St.-Germain was signed with Austria in September 1919, the Treaty of Neuilly with Bulgaria in November 1919, the Treaty of Trianon with Hungary in June 1920, and the Treaty of Sevres with the Ottoman Empire in August 1920.

Provisions of the treaties that officially ended World War I stripped the Central Powers of territory and arms and required them to pay reparations. Germany was punished especially severely. One clause in the Treaty of Versailles forced Germany to accept responsibility for causing the war.

Under the Treaty of Versailles, Germany gave up territory to Belgium, Czechoslovakia, Denmark, France, and Poland and lost its overseas colonies. France gained control of coal fields in Germany's Saar Valley for 15 years. An Allied military force, paid for by Germany, was to occupy the west bank of the Rhine River for 15 years. Other clauses in the treaty limited Germany's armed forces and required the country to turn over war materials, ships, livestock, and other goods to the Allies. A total sum for reparations was not set until 1921. At that time, Germany received a bill for about $33 billion.

The Treaty of St.-Germain and the Treaty of Trianon reduced Austria and Hungary to less than a third their former area. The treaties recognized the independence of Czechoslovakia, Poland, and a kingdom that later became Yugoslavia. Those new states, along with Italy and Romania, received territory that had belonged to Austria-Hungary. The Treaty of Sevres took Mesopotamia (later renamed Iraq), Palestine, and Syria away from the Ottoman Empire. Bulgaria lost territory to Greece and Romania. Germany's allies also had to reduce their armed forces and pay reparations.

The postwar world. The peacemakers found it impossible to satisfy the hopes and ambitions of every nation and national group. The settlements they drew up disappointed both the victors and the defeated powers.

In creating new borders, the peacemakers considered the wishes of national groups. However, territorial claims overlapped in many cases. For example, Romania gained a chunk of land with a large Hungarian population, and parts of Czechoslovakia and Poland had many Germans. Such settlements heightened tensions between countries. In addition, some Arab nations were bitter because they had failed to gain independence.

Certain borders created by the peace settlements made little economic sense. For example, the new countries of Austria and Hungary were small and weak and unable to support themselves. They had lost most of their population, resources, and markets. Austria's largely German population had wanted to unite with Germany. But the peace treaties forbade that union. The peacemakers did not want Germany to gain territory from the war.

Among the European Allies, Britain entered the postwar world the most content. The nation had kept its empire and control of the seas. But Britain worried that the balance of power it wanted in Europe could be upset by a severely weakened Germany and a victory by the Communists in a civil war in Russia. France had succeeded in imposing harsh terms on Germany -- its traditional foe -- but not in safeguarding its borders. France had failed to obtain a guarantee of aid from Britain and the United States in the event of a German invasion. Finally, Italy had gained less territory than it had been promised and felt it deserved.

In the United States, the Senate reflected public opinion and failed to approve the Treaty of Versailles. It thereby rejected President Wilson. The treaty would have made the United States a member of the League of Nations. Many Americans were not yet ready to accept the responsibilities that went along with their country's new power. They feared that the League of Nations would entangle the country in European disputes.

The Treaty of Versailles imposed harsher terms than Germany had expected. The responsibility of having accepted those terms weakened Germany's postwar government. During the 1930's, a strongly nationalist movement led by Adolf Hitler gained power in Germany. Hitler promised to ignore the Treaty of Versailles and to avenge Germany's defeat in World War I. In 1939, Germany invaded Poland. World War II had begun.