The Missouri Army National Guard is a component of the United States Army

United States Army

The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...

 and the United States National Guard

United States National Guard

The National Guard of the United States is a reserve military force composed of state National Guard militia members or units under federally recognized active or inactive armed force service for the United States. Militia members are citizen soldiers, meaning they work part time for the National...

. Nationwide, the Army National Guard

Army National Guard

Established under Title 10 and Title 32 of the U.S. Code, the Army National Guard is part of the National Guard and is divided up into subordinate units stationed in each of the 50 states, three territories and the District of Columbia operating under their respective governors...

comprises approximately one half of the US Army's available combat forces and approximately one third of its support organization. National coordination of various state National Guard units are maintained through the National Guard Bureau.

The National Guard may be called into federal service in response to a call by the President

President of the United States

The President of the United States of America is the head of state and head of government of the United States. The president leads the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces....

 or Congress

United States Congress

The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....

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The Missouri Army National Guard is composed of approximately 9,039 soldiers (in the 2009 fiscal year), and maintains armories in 63 communities.
Missouri Army National Guard units are trained and equipped as part of the United States Army.