Which President became the first to be impeached in U.S. history?

Andrew Johnson became the first president to be impeached in U.S. history in 1868. His impeachment was largely a result of his disagreements with Congress during the Reconstruction Era following the Civil War. Johnson's policies were viewed as too lenient towards the Southern states that had seceded, and he faced opposition from the Radical Republicans in Congress who sought to implement stricter measures for the reintegration of these states. The immediate catalyst for his impeachment was his violation of the Tenure of Office Act by attempting to remove Edwin M. Stanton, the Secretary of War, from his position without congressional approval. This act was seen as an infringement on the powers of Congress, thereby provoking the impeachment proceedings. Ultimately, Johnson was acquitted by just one vote in the Senate, but his impeachment marked a significant moment in U.S. political history, establishing a precedent for the impeachment process.