The compromises made before the Civil War (1861–1865) did not ameliorate the growing tensions between the North and the South. The main area of contention was slavery. It existed in the South, and the South wanted to protect it and spread it into new areas. The Founding Fathers had chosen not to deal with the slavery issue; they knew that it was too explosive of a subject. In 1848, however, the United States gained huge territories from Mexico after its victory. The acquisition of those territories unleashed and exacerbated latent sectional strife that finally ended in war.

By 1856, tensions had become so high that a congressman from South Carolina beat a senator from Massachusetts with his cane. There were, in fact, no national leaders by 1860. For example, Henry Clay, the Great Compromiser, died in 1852.

The Compromise of 1850 allowed California to enter as a free state. In return, the South received a stronger fugitive slave law. Southerners were angry that some Northerners helped the underground railroad.

Another attempt at compromise was the Kansas-Nebraska Act of 1854. This called for settlement of the slavery question by means of popular sovereignty—allowing the people of each territory to choose. This actually produced a mini civil war in Kansas as pro-slavery and anti-slavery forces fought each other.

Because of political disagreements on the slavery issue, a new political party emerged in the North—the Republican Party. This party, which was against slavery, won the presidential election of 1860 with Abraham Lincoln. Most Southern states then left the Union, and the Civil War started in 1861.