America - choose a jigsaw puzzle to solve

The United States of America (USA), commonly known as the United States (U.S.) or America, is 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 325 million people , the United States is the world 's third- or 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 . Forty-eight states and the capital's federal district are contiguous and in North America between Canada and Mexico . The state of Alaska is in the northwest corner of North America , bordered by Canada to the east and across the Bering Strait from Russia to the west . The state of Hawaii is an archipelago in the mid-Pacific Ocean . The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea , stretching across nine official time zones. The extremely diverse geography , climate , and wildlife of the United States make it one of the world 's 17 megadiverse countries . Paleo-Indians migrated from Russia to the North American mainland at least 15,000 years ago. European colonization began in the 16th century .