The United States of America, also known as the United States, the U.S., the U.S.A., the U.S. of A., The States and America, is a country in North America that extends from the Atlantic Ocean to the Pacific Ocean and shares land borders with Canada and Mexico. The United States is a federal republic, with its capital in Washington, D.C. At over 3.7 million square miles (over 9.5 million km²), the U.S. (including its non-contiguous and overseas states and territories) is the third or fourth largest country by total area, depending on whether China's figures include its disputed areas. It is the world's third most populous nation, with over 300 million people, as well as the world's most populous Christian-majority nation, with members representing all major denominations.