Lincoln presided over the Union victory in the American Civil War, which dominated his presidency. Lincoln took office following the 1860 presidential election, in which he won a plurality of the popular vote in a four-candidate field. Almost all of Lincoln's votes came from the Northern United States, as the Republicans held little appeal to voters in the Southern United States. A former Whig, Lincoln ran on a political platform opposed to the expansion of slavery in the territories. Lincoln, a former Whig Congressman, emerged as a major Republican presidential candidate following his narrow loss to Democrat Stephen A. Douglas in the 1858 Senate election in Illinois. Though he lacked the broad support of Republican Senator William H. Seward of New York, Lincoln believed that he could emerge as the Republican presidential nominee at the convention after multiple ballots.