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The United States of America (USA), generally recognized as the United States of America, is a national republic comprised of 50 states, a federal district, five major self-governing regions, and several territories. At 3.8 million square miles, the United States is the world's third- or fourth-largest country by total area and just fractionally smaller than the whole continent of Europe's 3.9 million square miles. With a population of over 325 million people, the U.S. is the third-most populous country.