Impeachment: This is a process where an official, such as the president, is accused of unlawful activity and which may lead to their removal from office. In this context, it's important because President Andrew Johnson was impeached for violating the Tenure of Office Act.
Reconstruction Era: This is a period after the Civil War when Southern states were reorganized and reintegrated into the Union. The Tenure of Office Act was part of many laws passed during this time.
Andrew Johnson: He was the 17th President of United States who assumed presidency after Lincoln's assassination. His violation and impeachment due to Tenure Of Office Act is significant in US history.