The United States of America is a federal republic of North America made up of fifty states and a federal district. The forty-eight contiguous states and the Washington D.C. district (the federal capital) occupy the central strip of North America between Canada and Mexico and are bordered by the Atlantic Ocean to the east and the Pacific Ocean to the west. With 9850476 km² in total and approximately 331 million inhabitants, the United States is the fourth country in the world by area and third by population. The geography and climate of the United States is extremely diverse, with deserts, plains, forests, and mountains that are also home to a huge variety of wildlife. It is one of the most multi-ethnic and multicultural nations in the world, a large-scale product of immigration from many countries.