The United States of America is a large country in North America, often referred to as the "USA," the "U.S.," the "United States," "America," or simply "the States." It has a land area of about 9.6 million km2 (about half the size of Russia and about the same size as China). It also has the world's third-largest population, with more than 320 million people. It includes densely populated cities with sprawling suburbs and vast uninhabited areas of natural beauty. Representing the world's single largest economy with its history of mass immigration dating from the 17th century, it is a "melting pot" of cultures from around the world.