Article One of the United States Constitution
Congress has several powers related to war and the armed forces. Under the War Powers Clause, only Congress may declare war, but in several cases it has, without declaring war, granted the President the authority to engage in military conflicts. Five wars have been declared in United States' history: the War of 1812, the Mexican–American War, the Spanish–American War, World War I and World War II. Some historians argue that the legal doctrines and legislation passed during the operations against Pancho Villa constitute a sixth declaration of war. Congress may grant letters of marque and reprisal. Congress may establish and support the armed forces, but no appropriation made for the support of the army may be used for more than two years. This provision was inserted because the Framers feared the establishment of a standing army, beyond civilian control, during peacetime. Congress may regulate or call forth the state militias, but the states retain the authority to appoint officers and train personnel. Congress also has exclusive power to make rules and regulations governing the land and naval forces. Although the executive branch and the Pentagon have asserted an ever-increasing measure of involvement in this process, the U.S. Supreme Court has often reaffirmed Congress's exclusive hold on this power (e.g. Burns v. Wilson, 346 U.S. 137 (1953)). Congress used this power twice soon after World War II with the enactment of two statutes: the Uniform Code of Military Justice to improve the quality and fairness of courts martial and military justice, and the Federal Tort Claims Act which among other rights had allowed military service persons to sue for damages until the U.S. Supreme Court repealed that section of the statute in a divisive series of cases, known collectively as the Feres Doctrine.