Southern slave states seceded to form the Confederate States of America, including Tennessee, but Johnson remained firmly with the Union. He was the only sitting senator from a Confederate state who did not resign his seat upon learning of his state's secession. In 1862, Lincoln appointed him as Military Governor of Tennessee after most of it had been retaken. In 1864, Johnson was a logical choice as running mate for Lincoln, who wished to send a message of national unity in his re-election campaign; and became vice president after a victorious election in 1864.
Johnson implemented his own form of Presidential Reconstruction, a series of proclamations directing the seceded states to hold conventions and elections to reform their civil governments. Southern states returned many of their old leaders and passed Black Codes to deprive the freedmen of many civil liberties, but Congressional Republicans refused to seat legislators from those states and advanced legislation to overrule the Southern actions. Johnson vetoed their bills, and Congressional Republicans overrode him, setting a pattern for the remainder of his presidency.[b] Johnson opposed the Fourteenth Amendment which gave citizenship to former slaves. 