The United States of America (USA), commonly referred to as the United
States (US), America or simply the States, is a federal republic
consisting of 50 states and a federal district. The 48 contiguous states
and the federal district of Washington, D.C., are in central North
America between Canada and Mexico. The state of Alaska is the
northwestern part of North America and the state of Hawaii is an
archipelago in the mid-Pacific. The country also has five populated and
nine unpopulated territories in the Pacific and the Caribbean. At 3.79
million square miles (9.83 million km2) in total and with around 317
million people, the United States is the fourth-largest country by total
area and third largest by population. It is one of the world's most
tethnically diverse and multicultural nations, the product of
large-scale immigration from many countries. The geography and climate
of the United States is also extremely diverse, and it is home to a wide
variety of wildlife.