War Powers Act, the common name for the War Powers Resolution, was passed by Congress in 1973 as a check on the U.S. president's war powers. It requires that the president, upon ordering any military forces into combat without a declaration of war, formally notify Congress of the action within 48 hours. In addition, the combat action must end within 60 days unless Congress authorizes a longer commitment. Congress can order immediate removal of forces by adopting a concurrent resolution (a resolution expressing the sentiments of both houses and not subject to presidential approval).
The War Powers Act was adopted near the end of the Vietnam War, when dissatisfaction with the undeclared war was high. Many in Congress believed that the United States was drawn into the conflict partly because the president had what they believed to be excessive power to take United States forces into combat.