Final answer:
The dispute between President Andrew Johnson and Congress exemplifies the constitutional principle of separation of powers, which requires branches of government to work together and prevents any single branch from becoming too powerful.
Step-by-step explanation:
The dispute between President Andrew Johnson and Congress during the Reconstruction Era illustrates the constitutional principle of separation of powers. This principle is highlighted by the checks and balances between the legislative and executive branches of the government. The clash occurred because President Johnson, who favored a lenient approach to Reconstruction and retaining control of it within the executive branch, often found himself at odds with the Republican-dominated Congress, which sought more stringent measures to transform the South and protect the rights of freedmen. This led to the impeachment of Johnson, a process involving different government branches working to check each other's power.
Reconstruction issues like citizenship and equality dominated the political landscape of the time. As part of their bid to control Reconstruction, Congress passed significant legislation such as the Civil Rights Act of 1866 and the Reconstruction Act, which were met with resistance by Johnson. His vetoes were overridden by Congress, demonstrating the legislative branch's resolve to assert its authority. Eventually, the conflict resulted in Congress passing the Tenure of Office Act and subsequently impeaching Johnson for violating it.
Ultimately, Johnson's impeachment underlines the dynamic tension inherent in the U.S. political system where exclusively neither Congress nor the President can dictate policies. The system necessitates cooperation and occasionally sparks conflicts, such as the one during the Reconstruction Era, which reveal the importance and challenge of the separation of powers in practical governance.