The militia of this State consists of all able-bodied persons over seventeen years of age who are: citizens of the United States residing within this State; citizens of the United States bound by law, lawful order, or contract to serve in the militia or military forces of this State; or persons who have declared their intention to become citizens of the United States and are bound by law, lawful order, or contract to serve in the militia or military forces of this State. The militia is divided into three classes: the National Guard, the organized militia, and the unorganized militia.