In the 1850s the debate over slavery spread into all areas of the nation's political business. The legislative struggle had begun with the Missouri Compromise of 1820, which banned slavery in new territories lying north of Missouri’s southern boundary. From that point on, a bitter conflict arose whenever settlement or war added new territory to the United States. As historian David M. Potter explains,

The history of the slavery contest was a record of paroxysms arising from territorial rivalry, and of lulls following upon territorial compromise. . . . This cycle always began with the acquisition or opening of a new territory. Such an event proved the signal for a conflict between slavery expansionists and exclusionists. As the violence of their contest increased so far as to threaten the security of the country, moderates and Unionists became alarmed and intervened to impose some sort of territorial adjustment, whereupon the...