The conflict that was mainly responsible for bringing about the passage of the War Powers Act was the Vietnam War. The act was passed in 1973, just as that war was winding down from the American point of view.
The Vietnam War helped to make Congress feel as if it was being left out of the loop of decisions to commit troops to things that were wars in all but name. The Constitution says that only Congress has the right to declare war, but American presidents had gotten the US deeply involved in Vietnam without any declaration of war. The Congress felt that it needed to take back some of its constitutional responsibilities. Therefore, it passed the War Powers Act. This act was meant to prevent the president from sending troops into combat for long periods of time without Congressional approval.