The National Guard is a reserve force in the United States military. Normally it is called upon to keep order in domestic emergencies, but it can also be used for other functions, including being called up to fight in foreign wars.
Both the Vietnam War and the Iraq War have seen a calling up of National Guard troops. Another recent calling out of the guard would be for Hurricane Katrina and to help free up border patrol agents by assuming responsibility for their more mundane tasks. Each state in the country has its own National Guard.
There are two sections to the National Guard: The Army National Guard and the Air National Guard. All Army National Guard recruits receive the same basic training that soldiers in the regular Army do, and all Air National Guard recruits receive the same training as regular Air Force personal.
Like the reserves, members of the National Guard drill one weekend per month at a local unit.