Following the Mexican War, questions arose as to the future of the territories that were acquired from Mexico. These territories included California, New Mexico and Arizona, among others. The main concern was statehood and whether slavery would be allowed in the new states. Obviously, the South in general was all for southern states’ rights and slavery expansion, and they advocated admitting the new territories as slave states. The North, on the other hand, was not as quick to want to give up the possibility of acquiring another free state for the advancement of the economy. The debate that ensued was one of the most significant and hard-fought debate that led to the Civil War.

There were other issues that confronted Congress. The House had voted to outlaw slavery in the District of Columbia, and had passed the Wilmot Proviso (which did fail in the Senate thanks to Sen. John C. Calhoun). Also, President Zachary Taylor had vowed to be president of all of the United States, not just the South, and he angered many radical, pro-slavery southerners with some of his pro-northern policies. Taylor also denounced any talk of secession.

With debates rising, senators Henry Clay, Daniel Webster and Calhoun, the Big Three as they were called, made their ideas known. Clay, who was the first to speak, declared that a compromise is the only solution to this problem, and both sides should concede to some point. Calhoun denounced Clay’s compromising initiative and threatened secession. Webster, who was usually a foe of Clay, agreed with him saying that preserving the Union was the most important issue, and compromise was the only was to do it.

With the death of Calhoun, just a month after his speech, and the death of Zachary Taylor (no, he was not poisoned) in 1850, the Clay's Compromise of 1850 was enacted by Congress and signed by the new president, Millard Fillmore. The Compromise had five provisions. Two favored the North’s interests, one was seemingly neutral, and two favored slave holders in the South. The first two admitted California as a free state and abolished slavery in the District of Columbia. The third left the slavery question in the other territories of New Mexico and Arizona up to the settlers, in accordance with the notion of popular sovereignty. The fourth merely compensated Texas settlers for further expanding into new territories, thus strengthening slave holders there.

The final measure was the Fugitive Slave Act, which stated, "aid to escaping slaves in the form of food, shelter, or other assistance was a federal crime, punishable by a $1,000 fine and six months in prison. Constitutional guarantees such as a trial by jury were simply ignored" (Davis, 105). It also created a bounty system to help create incentive among Northerners to aid Southern slave catchers in retrieving their "property." Thus, no escaped slave could truly be safe in the North.

This provision of the Compromise of 1850 was by far the most controversial, setting off a new wave of abolitionism and anti-South sentiment. Even many who were content to see slavery continue were now seeing this as a governmental endorsement of kidnapping. The Fugitive Slave Law and the notion of popular sovereignty haunted the Union from that point into the Civil War.