The underlying source of conflict between president Johnson and the Radical Republicans in congress was caused by their belief that Johnson was a Southern sympathizer who would undermine congress plans for Reconstruction. Johnson favored allowing the confederate states back in the Union if a certain percentage of the population would swear allegiance to the Union. In late February 1868, eleven articles of impeachment were brought against Andrew Johnson over political and ideological differences between the president and congress, and he was impeached.