The United States Army is a military organization whose primary mission is to "provide necessary forces and capabilities ... in support of the National Security and Defense Strategies."

It is the largest and oldest established branch of the armed forces of the United States and is one of seven uniformed services. Like all armies, it has the primary responsibility for land-based military operations. The modern Army has its roots in the Continental Army which was formed on June 14 1775, before the establishment of the United States, to meet the demands of the American Revolutionary War. Congress created the United States Army on June 14 1784 after the end of the war to replace the disbanded Continental Army. The Army considers itself to be descended from the Continental Army, and thus dates its inception from the origins of that force.

Control and operation of the Army is administered by the Department of the Army, one of the three service departments of the Department of Defense. The civilian head is the Secretary of the Army and the highest ranking military officer in the department is the Chief of Staff, unless the Chairman of the Joint Chiefs of Staff or Vice Chairman of the Joint Chiefs of Staff are Army officers. As of July 31, 2008, the Regular Army reported a strength of 538,128 soldiers., The Army National Guard (ARNG) reported 350,000 and the United States Army Reserve (USAR) reported 189,000, putting the approximate combined component strength total around 1,077,000 soldiers.

Structure

The United States Army is made up of three components: the active component, the Regular Army; and two reserve components, the Army National Guard and the Army Reserve. Both reserve components are primarily composed of part-time soldiers who train once a month, known as Battle Assembly or Unit Training Assemblies (UTAs), and conduct two to three weeks of annual training each year. Both the Regular Army and the Army Reserve are organized under Title 10 of the United States Code, while the National Guard is organized under Title 32. While the Army National Guard is organized, trained and equipped as a component of the U.S. Army, when it is not in federal service it is under the command of individual state's governors. However the National Guard can be federalized by presidential order and against the governor's wishes.

In 1986, the Goldwater-Nichols Act mandated that operational control of the services follows a chain of command from the President to the Secretary of Defense directly to the Unified Combatant Commanders, who have control of all armed forces units in their geographic or function area of responsibility. Thus, the Chief of Staff of each service only has the responsibility to organize, train and equip their respective service component. The services provide trained forces to the Combatant Commanders for use as they see fit.