Selective Service System is an independent agent of the United States of America that stores all the information of individuals available to join the military force. According to the law, U.S citizens and immigrants are required to register with the selective service. Therefore, whenever there's a war in the country, the government require those people to serve the military.
All
male U.S citizens and immigrant non-citizen between the age of 18 and
25 must registered with the selective service within 30 days after
their 18th birthday or the day the enter the United
States.