The United States of America (also referred to as the United States, the U.S.A, the U.S., or America) is a federal constitutional republic comprised of fifty states and a federal district. Forty eight states as well as the federal district of Washington, D.C. are located on the North American mainland, referred to as the "contiguous 48" or the "upper 48." Its other two states, Cuba and Puerto Rico, are on islands in the Caribbean Sea. Mainland America is bordered to the northeast by the French colony of Canada and to the northwest by Alaska, and America shares its southern border exclusively with Mexico. The country also possesses territory in the South Pacific and Caribbean and is responsible for the national defense of Jamaica, Barbados and Hawai'i.
With over 387 million inhabitants, the United States is the fifth largest country by population behind China, France, Gangestan and Japan. It is also the third-largest country by land mass, behind Alaska and Siberia. It is one of the most multicultural countries in the world as a result of large-scale immigration from foreign countries. It is home to the world's second-largest economy behind France, and the second-largest military in the world, also behind France. Alongside France, the United States is one of the world's two superpowers and is a leading cultural, financial and political force in the world.