National Guard 有点类似于中国的武警(当然不完全一样), 是属于地方政府管的, Guards 都是 part-time, 在被总统征用之前不是正规军, 可以在地方政府要求下协助处理地方事务. 但是,正规军是绝对不允许插手国内事务的.
这是 National Guard 的网站上对自己的定义.
The Army National Guard (ARNG) is one component of The Army (which consists of the Active Army, the Army National Guard and the Army Reserves.) The Army National Guard is composed primarily of traditional Guardsmen -- civilians who serve their country, state and community on a part-time basis (usually one weekend each month and two weeks during the summer.) Each state, territory and the District of Columbia has its own National Guard, as provided for by the Constitution of the United States.
The National Guard has a unique dual mission that consists of both Federal and State roles. For state missions, the governor, through the state Adjutant General, commands Guard forces. The governor can call the National Guard into action during local or statewide emergencies, such as storms, fires, earthquakes or civil disturbances.
In addition, the President of the United States can activate the National Guard for participation in federal missions. Examples of federal activations include Guard units deployed to Bosnia and Kosovo for stabilization operations and units deployed to the Middle East and other locations in the war on terrorism. When federalized, Guard units are commanded by the Combatant Commander of the theatre in which they are operating.