What was the main cause of thr impeachment of President Johnson in 1868?

The primary charge against Johnson was that he had violated the Tenure of Office Act, passed by Congress in March 1867 over Johnson's veto. ... Specifically, he had removed from office Edwin Stanton, the secretary of war whom the act was largely designed to protect.

Explanation:

demand is the need and oportunity to buy a given good or service.