Andrew Johnson was the 17th President of the United States, serving from 1865 to 1869. He became president after the assassination of Abraham Lincoln. Johnson, a Southern Democrat, faced the challenge of rebuilding the nation during the difficult period of Reconstruction following the Civil War. His approach to integrating the Southern states back into the Union was controversial and often met with resistance. Johnson's presidency was marked by conflict with Congress, particularly over issues of civil rights and the treatment of freed slaves. His opposition to the Radical Republicans led to his impeachment in 1868, making him the first U.S. president to be impeached, though he was acquitted by one vote.