In the United States, the state of North Dakota is changing the rules for its National Guard so that retired military personnel can be mobilized for service during a local emergency. This only involves retired NCOs, as officers are already covered by a similar program. There are over 2,000 retired military personnel in the state eligible for service under the new proposal. When activated, usually only for weeks, or months, the retired (after 20 or more years) troops would quickly join local Guard units and deal, usually, with a natural disaster. The retired troops would make a few bucks for the time they were on duty, but they would bring with them decades of military experience. Some of those retired troops would also have experience with National Guard service, but many retire from that because family and job demands don't leave enough time for regular Guard duties (one weekend a month, and two weeks during the Summer, of active duty and training). The North Dakota experiment is being closely watched by other states, because if the idea works, it would provide states low cost/high quality personnel when they need them most.
The National Guard is a direct descendent of the American colonial militia, and is controlled by the state governor, for local emergencies, in peace time. Over the years, the laws have changed so that it is easier for the federal government to "federalize" state guard units at times when the nation is not at war. The "war on terror" has caused many National Guards troops to be called up for extended periods. And many of them are then given jobs other than the ones they trained for (a lot of National Guards soldiers are just used for standing guard.)
But there is more to the National Guard. Most American men are unaware that they are in the army, or, as described by the Militia Act of 1903 (popularly known as the Dick Act), the unorganized militia. The main purpose of the Dick Act was to sort out over a century of confusion over the relationship between the state militias (now known as the National Guard) and the federal forces. The 1903 law was the first of many laws hammered out to create the system now in use. But in the last century, not much attention has been paid to the little known "unorganized militia" angle. This force contained every able-bodied adult male who was not a part of the organized militia. The 1903 law legalized the right not to be part of the organized militia, because a 1792 law had mandated that every adult male be part of the militia. The problem was, most men didn't want to be bothered. To deal with this, state governors created two classes of militia; paid (who trained and were armed and organized into units) and unorganized (everyone else.)
The militia is a state institution, and predates the founding of the United States. It harkens back to the ancient tribal practice, where every able bodied male turned out to defend the tribe. During the colonial period, this really only meant anything in frontier areas, where hostile Indians sometimes required the use of an armed militia force. In the late 18th century, only about ten percent of American families possessed a firearm, usually a musket or shotgun. Weapon ownership was much more common on the frontier, and in more settled areas, men with muskets often joined the organized militia more to be with their hunting buddies, than to prepare for war. The urban militia was sometimes used as a paramilitary force, when there was civil disorder or some kind of natural disaster. During the American Revolution, the militia served mainly as a police force, especially since about a third of the population were loyalists.
Therefore, if you are an adult American male between the ages of 17 and 45, you are part of the militia, whether you knew it or not, whether or not you want to be, and whether or not you are armed. Just so you know.