<P> 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 . 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 . </P> <P> During the War of 1812, an invasion of Canada failed, and U.S. troops were unable to stop the British from burning the new capital of Washington, D.C. . However, the Regular Army, under Generals Winfield Scott and Jacob Brown, proved they were professional and capable of defeating a major invasion by the regular British Army in the Niagara campaign of 1814 . Between 1815 and 1860, the main role of the U.S. Army was fighting Native Americans in the West in the American Indian Wars, and manning coast artillery stations at major ports . The U.S. used regular units and many volunteer units in the Mexican - American War of 1846 - 48 . At the outset of the American Civil War, the regular U.S. Army was small and generally assigned to defend the nation's frontiers from attacks by Native Americans . Following the Civil War, the U.S. Army fought more wars with Native Americans, who resisted U.S. expansion into the center of the continent . </P> <P> A combined conscript and volunteer force, the National Army, was formed by the United States War Department in 1917 to fight in World War I. During World War II, the Army of the United States was formed as a successor to the National Army . The end of World War II set the stage for the ideological confrontation known as the Cold War . With the outbreak of the Korean War, concerns over the defense of Western Europe led to the establishment of NATO . During the Cold War, American troops and their allies fought communist forces in Korea and Vietnam (see containment). The 1980s was mostly a decade of reorganization . The Army converted to an all - volunteer force with greater emphasis on training and technology . By 1989, the Cold War was coming to a close . The Army leadership reacted by starting to plan for a reduction in strength . After Desert Storm, the Army did not see major combat operations for the remainder of the 1990s . After the September 11 attacks, and as part of the War on Terror, U.S. and other NATO forces invaded Afghanistan in 2001, replacing the Taliban government . The Army took part in the U.S. and allied 2003 invasion of Iraq . </P> <P> The Continental Army consisted of troops from all 13 colonies . When the American Revolutionary War began at the Battles of Lexington and Concord 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, for local defense, or the raising of temporary "provincial regiments" during specific crises such as the French and Indian War . As tensions with Great Britain increased in the years leading up to the war, colonists began to reform their militia in preparation for the potential conflict . Training of militiamen increased after the passage of the Intolerable Acts in 1774 . Colonists such as Richard Henry Lee proposed creating a national militia force, but the First Continental Congress rejected the idea . </P>

What moves did the united states take toward war in early 1917