The United States of America (USA or U.S.A.), commonly called the United States (US or U.S.) and America, is a federal republic consisting of fifty states and a federal district as well as several territories with differing degrees of autonomy. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is situated in the northwest portion of the continent, with Canada to its east and Russia to its west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean.
At 3.79 million square miles (9.83 million km2) and with around 315 million people, the United States is the third- or fourth-largest country by total area and the third-largest by both land area and population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The geography and climate of the United States is also extremely diverse and is home to a variety of species.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the Residence Act approved the creation of a capital district located along the Potomac River on the country's East Coast. As permitted by the U.S. Constitution, the District is under the exclusive jurisdiction of the United States Congress and is therefore not a part of any U.S. state.
The states of Maryland and Virginia each donated land to form the federal district, which included the preexisting settlements of Georgetown and Alexandria; however, Congress returned the Virginia portion in 1846. Named in honor of George Washington, the City of Washington was founded in 1791 to serve as the new national capital. Congress created a single municipal government for the whole District of Columbia after the American Civil War.