The Lincoln-Douglas debates were a series of seven debates in 1858 between Stephen Douglas, United States senator from Illinois, and Abraham Lincoln, the Republican who sought to replace Douglas in the Senate. The debates were mainly about slavery. Douglas defended his Kansas–Nebraska Act, which replaced the Missouri Compromise ban on slavery in the Louisiana Purchase territory north and west of Missouri with popular sovereignty, which allowed residents of territories such as the Kansas to vote either for or against slavery. Douglas put Lincoln on the defensive by accusing him of being a Black Republican abolitionist, but Lincoln responded by asking Douglas to reconcile popular sovereignty with the Dred Scott decision. Douglas' Freeport Doctrine was that residents of a territory could keep slavery out by refusing to pass a slave code and other laws needed to protect slavery. Douglas' Freeport Doctrine, and the fact that he helped defeat the pro-slavery Lecompton Constitution, made Douglas unpopular in the South, which led to the 1860 split of the Democratic Party into Northern and Southern wings. The Democrats retained control of the Illinois legislature, and Douglas thus retained his seat in the U.S. Senate (at that time senators were elected by the state legislatures, not by popular vote); however, Lincoln's national profile was greatly raised, paving the way for his election as president of the United States two years later.