The militia of the United States, as defined by the U.S. Congress, has changed over time. During colonial America, all able-bodied men of a certain age range were members of the militia, depending on each colony's rule. Individual towns formed local independent militias for their own defense. The year before the U.S. Constitution was ratified, The Federalist Papers detailed the Founding Fathers' paramount vision of the militia in 1787. The new Constitution empowered Congress to "organize, arm, and discipline" this national military force, leaving significant control in the hands of each state government.

A company is a military unit, typically consisting of 100–250 soldiers and usually commanded by a major or a captain. Most companies are formed of three to seven platoons, although the exact number may vary by country, unit type, and structure.