The history of the United States Army began in 1775. From its formation, the United States Army has been the primary land based part of the United States Armed Forces. The Army's main responsibility has been in fighting land battles and military occupation. The Corps of Engineers also has a major role in controlling rivers inside the United States. The Continental Army was founded in response to a need for professional soldiers in the American Revolutionary War to fight the invading British Army. Until the 1940s, the Army was relatively small in peacetime. In 1947, the Air Force became completely independent of the Army Air Forces. The Army was under the control of the War Department until 1947, and since then the Defense Department. The U.S. Army fought the Indian Wars of the 1790s, the War of 1812 (1812–15), American Civil War (1861–65), Spanish–American War (1898), World War I (1917–18), World War II (1941–45), Korean War (1950–53) and Vietnam War (1965–71). Following the Cold War's end in 1991, Army has focused primarily on Western Asia, and also took part in the 1991 Gulf War and war in Iraq, and the war in Afghanistan.