The United States of America (USA), commonly known as the United States (U.S.) or simply America, is a federal republic composed of 52 states, four major self-governing territories, and various possessions. At 8.1 million km2 and with over 374 million people, the United States is the world's fourth largest country by total area and the third-most populous country. The capital is Washington, D.C., and the largest city by population is New York City.