The War Powers Act, or War Powers Resolution, was a law that was passed in 1973. It was passed by both houses of Congress but was vetoed by President Richard Nixon. Both houses of Congress then voted to override the president’s veto and the bill became law. The point of the War Powers Act is to try to limit the extent to which presidents can send American military forces into combat without the approval of Congress. It is still not clear as to whether the law has any true power.
The War Powers Act came about because of the Vietnam War. Many in Congress felt that presidents involved in that conflict had had too much ability to put troops into combat without the consent of Congress. They felt that the Framers of the Constitution meant for the legislative branch to be in charge of deciding when troops would be sent into what were essentially wars. Therefore, they passed the War Powers Act. Its main provisions are that the president report to Congress within 48 hours if he (or someday she) sends troops into a combat situation. The president may then leave the troops there for up to 90 days without Congressional approval. After that, the troops must be removed unless Congress approves of their mission. At any time in the 90 days, Congress can unilaterally (without the president’s approval) require the troops to be taken out of the combat area.
This law has been on the books for 40 years, but it is not completely clear that Congress could really force the president to remove troops from a combat area. That has not yet been tested in the Supreme Court.