This chapter details the events that intensified sectional conflicts in the United States and led eleven Southern states to secede and form the Confederate States of America.

Section 1 discusses how old tensions between the North and South resurfaced as the war with Mexico opened new lands and new states joined the Union. The controversial Wilmot Proviso proposed that slavery would not be allowed in any of the newly acquired territories. Popular sovereignty—the idea that citizens of each new territory should decide the slavery issue for themselves—gained support from both North and South. When California applied to join the Union as a free state, however, Congress again split down sectional lines. Finally, Clay's Compromise of 1850 gave California its statehood as a free state and pro-slavery forces strong federal enforcement of a new Fugitive Slave Act. Antislavery activists organized the Underground Railroad to help enslaved persons escape their bondage. Sectional conflicts heightened over the transcontinental railroad when Senator Stephen Douglas hurried to organize the Kansas and Nebraska territories for a northern route. Douglas's Kansas-Nebraska bill proposed to repeal the Missouri Compromise and allow slavery in the new territories. The bill's passage set off a bloody territorial civil war between antislavery and pro-slavery settlers in Kansas. When violence spread to the floor of the Senate, shocked Northerners strengthened their resolve to fight the "barbarism of slavery."

Section 2 details events that increased sectional tensions in the late 1850s. Reactions to the Kansas-Nebraska Act created sectional divisions within the American Party and the Whigs. Former Whigs and Free-Soil members formed the Republican Party to oppose the expansion of slavery. In 1856 voters elected Democrat James Buchanan to the presidency, hoping that he could unify the nation. Soon after he was elected, however, sectional conflict intensified over a Supreme Court ruling that supported slavery in any territory. When Kansas applied for statehood as a slave state, violent reactions in Congress underscored how deeply the slavery issue had divided the nation. During the Illinois Senate race debates of 1858, Abraham Lincoln gained national recognition as he warned that slavery threatened "the existence of this Union." The next year John Brown led an insurrection against slaveholders. While many Northerners viewed Brown's actions as noble, most Southerners became convinced that Northerners were plotting the murder of slave holders.

Section 3 follows the events that severed the nation and ignited civil war. Debates over slavery finally split the Democrats, prompting the fractured party to run two candidates in the 1860 presidential election. With the Democratic vote split, Republican candidate Abraham Lincoln won the presidency. Seven Southern states responded to Lincoln's victory by voting to secede from the Union. Northern members of Congress worked to find a compromise that would hold the Union together. On the same day delegates from 21 states held a peace conference, delegates from the seceding states declared the Confederate States of America a new nation. At his inauguration in March 1861 Lincoln urged reconciliation, but by April Confederate troops had seized Fort Sumter. When Lincoln called up the Union troops, states in the Upper South decided to side with the Confederacy. Lincoln prepared for war by quickly taking steps to keep the slave-holding border states from seceding.