Why was Andrew Johnson impeached by the Radical Republicans?

Andrew Johnson was impeached primarily for attempting to violate the Tenure of Office Act by removing Edwin M. Stanton, the Secretary of War, from his position and attempting to replace him with a more sympathetic appointee. This act was designed to restrict the president's power to remove certain officeholders without the Senate's approval. Johnson's actions were viewed by the Radical Republicans as a direct challenge to congressional authority and a violation of the law, which ultimately led to his impeachment.

His efforts to undermine the Reconstruction policies put in place by Congress, along with his general opposition to the Radical Republicans' initiatives, contributed to the perception that he was unfit for office. The impeachment process underscored the intense political struggles during this period and the clash between Johnson's Lenient approach towards the South and the more radical vision of Congressional Reconstruction fostered by the Radical Republicans.