Marty The United States of America is a federal republic in North America consisting of 50 states, a federal district, five major self-governing territories, and various possessions. The United States is the world's third-largest country by total area and the third-largest by population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The capital is Washington, D.C., and the largest city by population is New York City.