Why did congress pass the tenure of the office act in 1867?

Congress passed the Tenure of Office Act in 1867 to limit the president's power to remove certain officeholders without Senate approval, largely as a reaction to President Andrew Johnson's attempts to dismiss Secretary of War Edwin Stanton. The Act aimed to protect federal officials who were appointed by previous administrations and to assert congressional authority over appointments. This legislation was part of the broader conflict between Congress and Johnson during Reconstruction and sought to ensure that the president could not unilaterally alter the government’s political balance. Ultimately, it contributed to Johnson's impeachment, as he violated the Act by removing Stanton from office.