What was The underlying reason for the impeachment of President Andrew Johnson was?

The underlying reason for the impeachment of President Andrew Johnson was his violation of the Tenure of Office Act, which restricted the president's power to remove certain officeholders without Senate approval. Johnson's attempt to dismiss Edwin M. Stanton, the Secretary of War, led to his impeachment by the House of Representatives in 1868. However, the broader context included his opposition to Reconstruction policies and his lenient approach toward the South after the Civil War, which created significant conflict with Congress. Ultimately, he was acquitted by the Senate and remained in office.