To enlist in any branch of the U.S. military, you must either be a U.S. citizen or a legal permanent resident with a green card physically living in the United States. Non-citizens can only join the military as an enlisted member.
For enlistment purposes, citizens of the United States include citizens of Guam, Puerto Rico, the U.S. Virgin Islands, the Northern Marianas Islands, American Samoa, the Federated States of Micronesia, and the Republic of the Marshall Islands, as well as the 50 states.
There are also additional requirements for enlistment. You must also have a high school diploma or general equivalency diploma (GED) to enlist. You must also meet the age limit requirements for the branch you enlist in. Everyone enlisting in the military must also take the Armed Services Vocational Aptitude Battery (ASVAB) exam, and meet the physical and medical requirements for the branch you want to join.