The United States faced its greatest crisis in the late 1850s as the slavery question tore the nation asunder. The Lincoln-Douglas Debates of 1858 brought Americans' divisions over slavery into sharp focus. Douglas insisted that a heterogeneous nation could survive only if each locality determined its own institutions. Lincoln replied that slavery must be placed "in the course of ultimate extinction" by prohibiting its further expansion.

The debates marked Lincoln's emergence as a leader who epitomized the Republican party's essential values: opposition to the expansion of slavery, devotion to free labor, and reverence for the Union. He also accepted without challenge many of the racial prejudices of his day, reflecting that antislavery sentiments and racism coexisted in the Republican Party and throughout the North.

Douglas's principle of Popular Sovereignty, which allowed a territory to decide whether to establish slavery, was as unacceptable to the South as Lincoln's position. After the Supreme Court ruled in the Dred Scott case (1857) that Congress could not bar slavery from any territory, Southern political leaders demanded that the federal government protect the institution throughout the West.

Sectional hostilities were intensified when abolitionist John Brown led an armed assault on the federal arsenal at Harper's Ferry, Virginia, as part of a plan to incite a slave rebellion. Brown's trial and execution made him a martyr to many in the North, while Southerners saw his raid as a portent of what they might expect under Republican rule.

In 1860 the Democratic Party split into Northern and Southern wings, the last great bond of Union to be shattered by the sectional conflict. Republican presidential candidate Lincoln carried the entire North and, winning virtually no votes in the slave states, was elected. Fearful for slavery's future in a Republican-dominated nation, the Lower South seceded from the Union. Within six weeks of Lincoln's inauguration, Civil War had begun.

The Impending Crisis Exhibition