The United States of America (USA), commonly known as the United States (U.S.) or America, was a federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles (9.8 million km2) and with over 300 million people, the United States was the world's third- or fourth-largest country by total area and the third-most populous. The capital is Washington, D.C., and the largest city by population is New York City.