The United States of America (USA), commonly referred to as the United States (U.S.), America, and sometimes the States, is a federal republic consisting of 50 states and a federal district. The 48 contiguous states and Washington, D.C., are in central North America between Canada and Mexico. The state of Alaska is located in 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 3.80 million square miles (9.85 million km2) and with around 318 million people, the United States is the world’s fourth-largest country by total area and third-largest by population. It is one of the world’s most ethnically 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.
The United States is a developed country and has the world’s largest national economy. The economy is fueled by an abundance of natural resources and high worker productivity. While the U.S. economy is considered post-industrial, it continues to be one of the world’s largest manufacturers. The country accounts for 37% of global military spending, being the world’s foremost economic and military power, a prominent political and cultural force, and a leader in scientific research and technological innovations.