Question

Under Congressional Reconstruction, after Southern states were readmitted to the Union, they were controlled by the US Senate. the ex-governors. the US military. the president.

Answer 1

The answer is the US military.
Every Huge decision that made by the United States military basically have to go with Senate confirmation.
This includes the decisions such as the decision to join the war,the decision to allocate budget, the decision to promote a certain military officer,  etc.