The continental United States has been inhabited for at least 15,000 years by Native Americans. After 16th-century European exploration and settlement, the English established new colonies, and gained control of others, in the eastern portion of the continent in the 17th and early 18th centuries. On 4 July 1776, at war with Britain over fair governance, thirteen of these colonies declared their independence; in 1783, the war ended in British acceptance of the new nation. Since then, the country has more than quadrupled in size: it now consists of 50 states, one federal district, and a number of overseas territories.

At over 3.7 million square miles (over 9.1 million km²), the U.S. is the third or fourth largest country by area, depending on the reckoning of the disputed areas of China. It is also the world's third most populous nation, with nearly 300 million people.