Andrew Johnson happens to be the 17th president of US. The confederate states of America refers to a group of states which supported slavery of Africans as their economy was dependant on Agriculture. The considered white people above the black.
Johnson was against slavery and did a great work to abolishment of slavery and re-joining of the confederate states. He was also against the concept of secession as when other states were forming confederate states including Tennessee, he stood firmly with the union.