 In early 1854 , Senator Douglas introduced his Kansas – Nebraska Bill , calling for popular sovereignty to determine whether the Kansas and Nebraska territories should enter the Union as slave or free states . Depending on the outcome of such elections , slavery might spread to territories closed to it under the Compromise of 1850 . In the debate over the bill , Benjamin defended this change as returning to " the traditions of the fathers " , that the federal government not legislate on the subject of slavery . He said that the South merely wished to be left alone . The bill passed , but its passage had drastic political effects , as the differences between North and South that had been settled by the Compromise were reopened . The Whig Party was torn apart North from South , with many Northern Whigs joining the new Republican Party , a group pledged to oppose the spread of slavery . Benjamin continued to caucus with the remains of the Whig Party through 1854 and 1855 , but as a member of a legislative minority , he had little influence on legislation , and received no important committee assignments . 
