The Legacy of the Mexican War drew Abraham Lincoln from his self-imposed political exile. In 1854 Illinois' Democratic Senator Stephen Douglas took up the issue of settling the western territories, which had festered since 1847.

While northern and southern politicians wrestled with the problem of organizing the west while maintaining a sectional political balance, settlers continued to stream westward. Northerners and southerners often took up residence in the same communities, and each expected to live according to the laws and conventions that had governed their previous home. These expectations often clashed, especially over the issue of human slavery.

Congress had delayed organizing these rapidly settled areas into territories because northern and southern factions entertained divergent, and potentially explosive, expectations for them. Many northerners saw the West as a haven for white settlers, free from competition with slave labor. Most Southerners expected that they could move west with their slave property without the threat of their emancipation.

Stephen Douglas broke this political deadlock with his Kansas-Nebraska Bill, which proposed to organize the territories of Kansas and Nebraska based upon "Popular Sovereignty," or the stated will of the settlers themselves. Thus the people were to decide if their territories were to be slave or free.

Douglas believed that his proposal drew upon the strength of the American Democratic Tradition, and it became law in the spring of 1854. But the Act quickly fanned the flames of the sectional crisis, driving northern and southern extremists to new lengths in their attempts to win the territories for their rival political systems.

In the North many Whigs and a substantial number of Democrats cried that Douglas' Act overturned the Missouri Compromise of 1820, which had banned slavery above the line extending from Missouri's southern border. Northerners already distrustful of southerners who had seemingly dominated national politics for a generation were quick to assume that the "Slave Power" had triumphed again.

These developments led to the rapid birth and development of the Republican Party, which came together around the fundamental issue of opposing slavery's western expansion. This issue summoned Abraham Lincoln back to public life, and the Republican Party brought his message to a national audience.