 The central issue in politics in the 1850s involved the extension of slavery into the western territories, which settlers from the Northern states opposed.The Whig Party split and collapsed on the slavery issue, to be replaced in the North by the new Republican Party, which was dedicated to stopping the expansion of slavery.Republicans gained a majority in every northern state by absorbing a faction of anti-slavery Democrats, and warning that slavery was a backward system that undercut democracy and economic modernization.