The United States of America, commonly referred to as the United States (U.S.) or America, is a constitutional federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions. The US is the world’s third largest country in size and population and one of the most ethnically diverse and multicultural relations. The capital city of US is Washington, DC and the largest city is the New York City. The population of US is approximately 318 million. The US is the largest economy in the world with most technologically advanced.