Who became president after the assassination of Abraham Lincoln?

After the assassination of Abraham Lincoln in 1865, Andrew Johnson, who was serving as vice president at the time, assumed the presidency. Johnson was a Southern Democrat from Tennessee and had been chosen as Lincoln's running mate in an effort to promote national unity during the Civil War. His ascension to the presidency marked a significant transition as he became responsible for leading the nation during the difficult Reconstruction era following the war.

Johnson's policies were often at odds with the Republican-led Congress, leading to significant political strife. His approach to Reconstruction sought to quickly reintegrate the Southern states, but it faced criticism for being too lenient towards former Confederates. This ultimately resulted in his impeachment, although he was acquitted by one vote.

Ulysses S. Grant, James A. Garfield, and Chester A. Arthur all served as president after Johnson, but they did not succeed Lincoln directly. Their presidencies occurred after a substantial period marked by Johnson's administration and the tumultuous issues of Reconstruction. Thus, Andrew Johnson is clearly the correct answer as the immediate successor to Abraham Lincoln following his assassination.