Before the European colonization of the Americas, a process that began at the end of the 15th century, the present-day continental U.S. was inhabited exclusively by various indigenous tribes, including Alaskan Natives, who arrived on the continent over a period that may have begun 35,000 years ago and may have ended as recently as 11,000 years ago. The first confirmed European landing in the present-day United States was by a Spaniard, Juan Ponce de Leon, who landed in 1513 in Florida, and as part of his claim, the first European settlement was established by Don Pedro Menendez de Aviles on the site of a Timucuan Indian village in 1565 at St. Augustine, Florida. The first successful English settlement was at Jamestown, Virginia, in 1607, followed in 1620 by the Pilgrims' landing at Plymouth, Massachusetts. In 1609 and 1617, respectively, the Dutch settled in part of what became New York and New Jersey. In 1638, the Swedes founded New Sweden, in part of what became Delaware, New Jersey, and Pennsylvania after passing through Dutch hands. Throughout the 17th and early 18th centuries, England (and later Great Britain) established new colonies, took over Dutch colonies, and split others. With the division of the Carolinas, in 1729, and the colonization of Georgia, in 1732, the British colonies in North America, excluding Canada, numbered thirteen. These thirteen colonies would be drawn closer together over the coming decades.

The Mayflower, which transported Pilgrims to the
New World, arrived in 1620.

Tensions between American colonials and the British during the revolutionary period of the 1760s and 1770s led to open military conflict in 1775. George Washington commanded the Continental Army during the American Revolutionary War (1775–1783) as the Second Continental Congress adopted the Declaration of Independence on 4 July 1776. The Second Continental Congress had been formed to confront British actions, and did create the Continental Army, but did not have the authority to levy taxes or make federal laws. In 1777, the Congress adopted the Articles of Confederation, uniting the states under a weak federal government, which operated from 1781 until 1788, when enough states had ratified the United States Constitution. The Constitution, which strengthened the union and the federal government, has since remained the supreme law of the land.

Presenting the Declaration of Independence to the Continental Congress

From 1803 to 1848, the size of the new nation nearly tripled as settlers (many entrenched with the concept of Manifest Destiny as an inevitable consequence of American exceptionalism) pushed beyond national boundaries even before the Louisiana Purchase. The expansion was tempered somewhat by the stalemate in the War of 1812, but was subsequently reinvigorated by victory in the Mexican–American War in 1848.

National Atlas map depicting dates of select territorial acquisitions. Full Oregon and other claims are not included.

As new territories were being incorporated, the nation was divided over the issue of states' rights, the role of the federal government, and, by the 1820s, the expansion of slavery. The Northern states were opposed to the expansion of slavery whereas the Southern states saw the opposition as an attack on their way of life, since their economy was dependent on slave labor. The failure to permanently resolve these issues led to the American Civil War, following the secession of many slave states in the South to form the Confederate States of America after the 1860 election of Abraham Lincoln. The 1865 Union victory in the Civil War effectively ended slavery, as well as settling the question of whether a state had the right to secede. The event was a major turning point in American history, with an increase in federal power.

The Battle of Gettysburg, a major turning point of the American Civil War. The victory of the Union kept the country united.

After the Civil War, an unprecedented influx of immigrants, who helped to provide labor for American industry and create diverse communities in undeveloped areas together with high tariff protections, national infrastructure building, and national banking regulations, hastened the country's rise to international power (although as WWI approached American politicians began embracing free trade). The United States subsequently gained new territories as a result of its growing power status, including the annexation of Puerto Rico after victory in the Spanish–American War, which marked the beginning of the U.S. as a major world power.

Landing at Ellis Island, 1902. Immigration helped spur the American economy.

At the start of the First World War, in 1914, the U.S. remained neutral; but, in 1917, the U.S. joined the Allied Powers, helping to turn the tide against the Central Powers. For historical reasons, American sympathies were very much in favor of the British and French, even though a sizable number of citizens, mostly Irish and German, were opposed to intervention. After the war, the Senate did not ratify the Treaty of Versailles, because of a fear that it would pull the U.S. into European affairs which President Washington had warned against. Instead, the country chose to pursue a policy of unilateralism that bordered at times on being isolationist.

An abandoned farm in South Dakota during the Great Depression, 1936.

During most of the 1920s, the U.S. enjoyed a period of unbalanced prosperity as farm prices fell and industrial profits grew. A rise in debt and an inflated stock market culminated in a crash in 1929, triggering the Great Depression, which with the New Deal, led to the rise of greater government intervention in the economy.

U.S. astronaut Buzz Aldrin on the moon, 1969.

The nation did not fully recover until 1941, when the U.S. was driven to join the Allies against the Axis after a surprise attack on Pearl Harbor by the Japanese. World War II was the costliest war in American history, but helped to pull the economy out of depression as the required production of military materiel provided much-needed jobs and women entered the workforce in large numbers for the first time.

After World War II, the United States and the Soviet Union became superpowers in an era of ideological rivalry dubbed the Cold War. The U.S. represented liberal democracy and capitalism, while the USSR represented communism and a centrally planned economy. The result was a series of proxy wars, including the Korean War, the Vietnam War, the tense nuclear showdown of the Cuban Missile Crisis, and the Soviet war in Afghanistan.

The perception that the U.S. was losing the space race spurred government efforts to raise proficiency in mathematics and science in schools and lead to President Kennedy's call for the United States to land "a man on the moon" by the end of the 1960s, which was realized in 1969.

Meanwhile, American society experienced a period of sustained economic expansion. At the same time, discrimination across the U.S., especially in the South, was increasingly challenged by a growing civil-rights movement headed by prominent African Americans such as Martin Luther King, Jr., which led to the abolition of the Jim Crow laws in the South.

After the fall of the Soviet Union in 1991, the United States continued to involve itself in military action overseas, such as the Gulf War.

Following the September 11, 2001, attacks, U.S. foreign policy focused on the threat of terrorist attacks. In response, the government under George W. Bush began a series of military and legal operations termed the War on Terror, beginning with the overthrow of Afghanistan's Taliban government in October 2001. Soon after, the War on Terror continued with the controversial 2003 invasion of Iraq, with support from 30 governments, which George W. Bush referred to as the 'Coalition of the Willing'. The reasons for which the war in Iraq was fought have been severely criticized, and the Bush administration later admitted having acted on flawed intelligence.