April 30, 1803

By a treaty signed on Apr. 30, 1803, the United States purchased from France the Louisiana Territory, more than 2 million sq km (800,000 sq mi) of land extending from the Mississippi River to the Rocky Mountains. The price was 60 million francs, about $15 million; $11,250,000 was to be paid directly, with the balance to be covered by the assumption by the United States of French debts to American citizens.

In 1762, France had ceded Louisiana to Spain, but by the secret Treaty of San Ildefonso (1800) the French had regained the area. Napoleon Bonaparte (the future Emperor Napoleon I) envisioned a great French empire in the New World, and he hoped to use the Mississippi Valley as a food and trade center to supply the island of Hispaniola, which was to be the heart of this empire. First, however, he had to restore French control of Hispaniola, where Haitian slaves under Toussaint L'Ouverture had seized power. In 1802 a large army sent by Napoleon under his brother-in-law, Charles Leclerc, arrived on the island to suppress the Haitian rebellion. Despite some military success, the French lost thousands of soldiers, mainly to yellow fever, and Napoleon soon realized that Hispaniola must be abandoned. Without that island he had little use for Louisiana. Facing renewed war with Great Britain, he could not spare troops to defend the territory; he needed funds, moreover, to support his military ventures in Europe. Accordingly, in April 1803 he offered to sell Louisiana to the United States.

Concerned about French intentions, President Thomas Jefferson had already sent James Monroe and Robert R. Livingston to Paris to negotiate the purchase of a tract of land on the lower Mississippi or, at least, a guarantee of free navigation on the river. Surprised and delighted by the French offer of the whole territory, they immediately negotiated the treaty.

Jefferson was jubilant. At one stroke the United States would double its size, an enormous tract of land would be open to settlement, and the free navigation of the Mississippi would be assured. Although the Constitution did not specifically empower the federal government to acquire new territory by treaty, Jefferson concluded that the practical benefits to the nation far outweighed the possible violation of the Constitution. The Senate concurred with this decision and voted ratification on Oct. 20, 1803. The Spanish, who had never given up physical possession of Louisiana to the French, did so in a ceremony at New Orleans on Nov. 30, 1803. In a second ceremony, on Dec. 20, 1803, the French turned Louisiana over to the United States.