The United States' territories are numerous.
The United States of America ( USA ) , commonly known as the United States ( U.S. ) or America , is a constitutional federal republic composed of 50 states , a federal district , five major self-governing territories , and various possessions . The United States embarked on a vigorous expansion across North America throughout the 19th century , displacing Native American tribes , acquiring new territories , and gradually admitting new states until it spanned the continent by 1848 .