The history of the United States Army began in 1775. 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), Mexican–American War (1846–48), American Civil War (1861–65), American Indian Wars (ended 1890), 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.
When the American Revolutionary War began in April 1775, the colonial revolutionaries did not have an army. Previously, each colony had relied upon the militia, made up of part-time civilian-soldiers. The initial orders from Congress authorized ten companies of riflemen and one field artillery battery. The first full regiment of Regular Army infantry, the 3rd Infantry Regiment, was not formed until June 1784. After the war, the Continental Army was quickly disbanded because of the American distrust of standing armies, and irregular state militias became the new nation's sole ground army, with the exception of a regiment to guard the Western Frontier and one battery of artillery guarding West Point's arsenal.
