The history of the United States begins with the arrival of human beings thousands of years ago. The first known inhabitants of what is now the United States are believed to have arrived over a period of several thousand years beginning sometime prior to 15,000–50,000 years ago by crossing Beringia into Alaska. Solid evidence of these cultures settling in what would become United States territory is dated to around 14,000 years ago.

Research has revealed much about the early Native American settlers of North America. Christopher Columbus' men were the first documented Old Worlders to land in the territory of what is now the United States when they arrived in Puerto Rico during their second voyage in the year 1493. Juan Ponce de León, who arrived in Florida in 1513, is credited as being the first European to land in what is now the continental United States, although some evidence suggests that John Cabot might have reached what is presently New England in 1498.

The coming of Europeans began the colonial history of the United States. The Thirteen Colonies, British colonies that would become the original US states, were founded along what is now the country's east coast beginning in 1607, but various other European powers also founded settlements in what would become US territory, both before and later. Due to growing dissatisfaction with British rule, the thirteen British colonies fought the British army in the American Revolutionary War of the 1770s and issued a Declaration of Independence in 1776. In early 1781, the Articles of Confederation and Perpetual Union of the States were established, six months before the end of hostilities in the Revolutionary War. Two years later, Britain officially recognized the sovereignty and independence of the United States in the Treaty of Paris. In the nineteenth century, westward expansion of United States territory began, encouraged by the belief in Manifest Destiny, in which the United States would occupy all of North America east to west, from the Atlantic to the Pacific Oceans. By 1912, with the admission of Arizona to the Union, the US reached that goal. The outlying states of Alaska and Hawaii were both admitted in 1959.

Ratified in 1788, the Constitution serves as the supreme law in organizing the government; the Supreme Court is responsible for upholding Constitutional law. Many forms of social progress started in the nineteenth century; those advancements have been widely reflected in the Constitution. Slavery was abolished in 1865 by the Thirteenth Amendment to the United States Constitution; the following Fourteenth and Fifteenth Amendments respectively guaranteed citizenship for all persons naturalized within US territory and voting for people of all races. In later decades, civil rights were extended to women and African-Americans, following effective lobbying from social activists. The Nineteenth Amendment prohibited gender discrimination in voting rights; later, the Civil Rights Act of 1964 outlawed racial segregation in public places.

The Progressive Era marked a time of economic growth for the United States, advancing to the Roaring Twenties. However, the Wall Street Crash of 1929 led to the Great Depression, a time of economic downturn and mass unemployment. Consequently, the U.S. government established the New Deal, a series of reform programs that intended to assist those affected by the Depression. The New Deal had varied success. However, once the US entered World War II in December 1941, the economy quickly recovered, so much that the US became a world superpower by the dawn of the Cold War. During the Cold War, the US and the Soviet Union were the world's two superpowers, but with the end of the Cold War and the collapse of the Soviet Union, the United States became the world's only superpower.