The United States of America is a large country in central and north-western 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 sq km (about half the size of Russia and about the same size as China). It also boasts the worlds third largest population after China and India, with over 300 million people. It includes both densely-populated cities with sprawling suburbs, and vast, uninhabited and naturally beautiful areas. With its history of mass immigration dating from the 17th century, it is a "melting pot" of cultures from around the world.