In 1854, Congress passed the Kansas-Nebraska Act, which repealed the Missouri Compromise, and allowed individual states and territories to decide for themselves whether to allow slavery. The law provoked violent opposition in Kansas and Illinois, and it gave rise to the Republican Party. This awakened Abraham Lincoln's political zeal once again, and his views on slavery moved more toward moral indignation. Lincoln joined the Republican Party in 1856.
In 1857, the Supreme Court issued its controversial decision Scott v. Sanford, declaring African Americans were not citizens and had no inherent rights. Though Abraham Lincoln felt African Americans were not equal to whites, he believed the America's founders intended that all men were created with certain inalienable rights. Lincoln decided to challenge sitting U.S. Senator Stephen Douglas for his seat. In his nomination acceptance speech, he criticized Douglas, the Supreme Court, and President Buchanan for promoting slavery and declared "a house divided cannot stand."