The first residents of what is now the United States emigrated from Asia over 15,000 years ago by crossing Beringia into what is now present-day Alaska. Archaeological evidence of these people, the ancestors of the Native Americans, dates back to 14,000 years ago.

Christopher Columbus was the first European to land in the territory of what is now the United States when he arrived in Puerto Rico in 1492. The subsequent arrival of settlers from Europe began the colonial history of the United States. The Thirteen English colonies that would become the original US states were founded along the east coast beginning in 1607. Spain, France and Russia also founded small settlements in what would become US territory.

The population of the Thirteen Colonies grew rapidly, reaching 50,000 by 1650, 250,000 by 1700, and 2.5 million by 1775. High birth rates and low death rates were augmented by steady flows of immigrants from Europe and slaves from the West Indies. Occasional small-scale wars involved the French and Indians to the north, and the Spanish and Indians to the south. Religion was a powerful influence on many immigrants, especially the Puritans in New England and the German sects in Pennsylvania, with boosts from the revivals of the First Great Awakening. The colonies by the 1750s had achieved a standard of living about as high as Britain, with far more self-government than anywhere else. Most free men owned their own farms and could vote in elections for the colonial legislatures, while local judges and local juries dispensed justice. Royal soldiers were rarely seen.

The colonists did not have representation in the ruling British government and believed they were being denied their constitutional rights as Englishmen whenever parliament tried to tax them. For many years, the home government had permitted wide latitude to local colonial governments. Beginning in the 1760s London demanded the colonists pay taxes; the main issue was not the money (the taxes involved were quite low) but the issue of who was in control. The new taxes on stamps in 1765 and later the tax on tea ignited a firestorm of opposition. The British responded with military force in Massachusetts, and shut down the system of local self government in what the colonists called the Intolerable Acts.

After fighting broke out in April 1775, the colonies ousted all royal officials and set up their own governments, which were led from Philadelphia by the Continental Congress and its commander in chief, General George Washington. The American Revolution escalated into all-out war. The new nation declared independence in July 1776 as the United States of America. After Americans captured the British invasion army in 1777, France became a military ally, and the war became a major international war with evenly balanced forces. With the capture of a second British invasion army at Yorktown in 1781, the British opened peace negotiations. The Treaty of Paris in 1783 proved highly favorable to the new nation.

The new national government proved too weak, so a Constitutional Convention was called in 1787 to create an alternative. The resulting Constitution of the United States, ratified in 1788, created a federal government based on the ideology of republicanism, equal rights, and civic duty. The first ten amendments known as the Bill of Rights quickly followed, guaranteeing many individual rights from federal interference. The new national government under President George Washington began operation in 1789, and built a strong economic system, designed by Alexander Hamilton, that settled the wartime debts, created a national bank and sought economic growth based on cities and trade, more than farming. Hamilton formed the Federalist Party to gain wide local support for the new policies, which were opposed by Thomas Jefferson.

The Jay Treaty of 1795 opened a decade of trade with Britain, which was at war with revolutionary France. The French feared British influence would undermine republicanism in the United States. Because Jefferson, Madison and others shared that fear, they set up an opposition party, and the First Party System based on voters in every state, began operation in the mid-1790s. Jefferson was elected president in 1800 and tried to coerce the British; he wanted the British to recognize America's neutral rights, stop the seizure ("impressment") of sailors on American ships, and quit arming hostile Indians in the West. When that failed the U.S. declared the War of 1812 against Britain. The war was militarily indecisive but guaranteed American independence and friendly relations with the British Empire, which controlled Canada.

With the Louisiana Purchase in 1803 westward expansion of the United States crossed the Mississippi River. This was encouraged by the belief in Manifest Destiny, by which the United States would expand east to west, reaching the Pacific after the conquest of Mexico in 1848. A series of revivals in the Second Great Awakening made many Americans actively religious, and stimulated many reform movements, including abolition of slavery. Rapid economic and population growth created a powerful nation, but tensions escalated between the slaveholding plantation South and the industrial North, which had long since abolished slavery. The South in 1861 tried to break away and form its own country, the "Confederacy," in response to threats to its peculiar institution—slavery. The Civil War lasting four years became the deadliest war in American history. Under the leadership of Republican Abraham Lincoln the rebellion was crushed, the nation reunified, the slaves freed, and the South put under Reconstruction for a decade.

Rapid economic growth, fueled by entrepreneurs who created great new industries in railroads, steel, coal, textiles, and machinery operated by millions of immigrants from Europe (and some from Asia), built new cities overnight, making the U.S. the world's leading industrial power. With Germany threatening to win World War I in part by sinking American ships, the U.S. entered the war in 1917, supplied the material, money and to a degree the soldiers needed to win. The U.S. partially dictated the peace terms, but refused to join the League of Nations, as it enjoyed unprecedented prosperity in the 1920s. The crash of 1929 started the worldwide Great Depression, which was long and severe for the entire country. A New Deal Coalition led by Franklin D. Roosevelt dominated national elections for years, and the New Deal in 1933-36 began a new era of federal regulation of the business, support for labor unions, and provision of relief for the unemployed and Social Security for the elderly.

The U.S. joined the Allied Forces of World War II in December 1941 after the Japanese attack on Pearl Harbor. Postwar hopes that the new United Nations would resolve the world's problems failed, as Europe was divided and the U.S. took the lead in the Cold War with a policy of containing Soviet expansion. Containment led to wars in Korea (a stalemate) and Vietnam (lost). Economic prosperity after the war empowered families to move to the suburbs and engage in a Baby Boom that pushed the population from 140 million in 1940 to 203 million in 1970. The industrial economy based on heavy industry gave way to a service economy featuring health care and education, as America led the way to a computerized world. The end of the Cold War came in 1991 as Soviet Communism collapsed. The U.S. was the only military superpower left, but it was challenged for economic supremacy by China, which remained on good terms with the U.S. as it embraced capitalism and by 2010 was growing much more rapidly than the U.S.

The Civil Rights Movement ended Jim Crow and empowered black voters in the 1960s, which allowed blacks to move into high government offices. However, the New Deal coalition collapsed in the mid 1960s in disputes over race and the Vietnam War. The Reagan Era of conservative national policies, deregulation and tax cuts took control with the election of Ronald Reagan in 1980. By 2010, political scientists were debating whether the election of Barack Obama in 2008 represented an end of the Reagan Era, or was only a reaction against the bubble economy of the 2000s, which burst in 2008 and became the Late-2000s recession with prolonged unemployment.