For the United States to undertake military action against those who committed the September 11, 2001, terrorist attacks, Congress either had to declare war against a specific country or countries, or it had to enact an authorization to use military force (AUMF). An AUMF is a joint resolution that grants the president wide authority to use the military against enemies of the United States. It can be directed against specific countries or against regions or groups. The AUMF was necessary because the 1973 War Powers Resolution limited the power of the president to use military force to sixty days without congressional approval. An AUMF extended that authority. Subsequent AUMFs were passed prior to the 2003 invasion of Iraq and the 2013 military strikes on Syria.