One of the main issues before the war was the debate over whether the states that wished to enter the Union would forbid or allow slavery. The slave states wished to add more states to preserve their representation in Congress, and the free states wanted slavery to be forbidden. The Kansas-Nebraska Act of 1854 created two territories and said that the inhabitants could choose the new state's position on Slavery. This lead to a race of immigration between the pro-slavery "Border Ruffians" and the "Free-Staters." John Brown, who would later lead the attack on Harper's Ferry, went to Kansas to attempt to outlaw slavery by force of arms. Under his leadership the two factions came into conflict in what was called "Bleeding Kansas." Two competing governments were started, and several constitutions were written. Eventually the Free-Staters prevailed and the people adopted the Wyandotte Constitution.
On February 15th, 1860 a bill was introduced into the Senate to admit Kansas into the Union under that constitution. The bill was delayed by the South for almost one year, but their power was broken on January 21st when ten Southern senators withdrew from the senate because several states had seceded. The South's power was gone, and the bill was passed 36 to 16 and was signed by the president on January 29th.
This episode showed that since many of the Southern states had seceded, the South had lost its power. The remaining slave holding states no longer had the power to resist the North, and it appeared that unless the North tried to conciliate them and preserve the Union, they too would be forced to secede.