United States

The territory of the present-day United States was inhabited for many thousands of years before European contact by a wide range of Indigenous peoples, including the mound-building cultures of the Mississippi and Ohio valleys, the Ancestral Puebloans of the Southwest, and the agricultural and hunting societies of the Eastern Woodlands, the Great Plains, the Pacific Northwest, and the Arctic. By the late fifteenth century, this population was organised into hundreds of distinct nations and confederacies, among them the Haudenosaunee (Iroquois), the Powhatan, the Cherokee, the Muscogee, the Lakota, the Navajo, and the Pueblo communities of the Rio Grande.

Sustained European colonisation began in the sixteenth century with Spanish settlement in Florida and the Southwest, followed by French activity along the Mississippi and Great Lakes, Dutch posts on the Hudson, and a series of English colonies established on the Atlantic seaboard between 1607 (Jamestown) and 1733 (Georgia). The colonial period was marked by displacement of Indigenous peoples through warfare and disease, the expansion of plantation agriculture, and the forced importation of enslaved Africans, particularly into the southern colonies. After Britain consolidated its position in North America at the close of the Seven Years' War in 1763, friction with the thirteen Atlantic colonies over taxation and self-government escalated into open revolt.

The Declaration of Independence was adopted on 4 July 1776, and the resulting War of Independence ended with British recognition of the new republic in the Treaty of Paris in 1783. The Constitution drafted at Philadelphia in 1787 took effect in 1789, establishing a federal republic with a separation of powers and, through the Bill of Rights of 1791, a written guarantee of civil liberties. Across the nineteenth century the country expanded westward through purchase, treaty, and conquest, including the Louisiana Purchase of 1803, the annexation of Texas, and the Mexican Cession of 1848. The unresolved question of slavery culminated in the Civil War of 1861 to 1865, after which the Thirteenth, Fourteenth, and Fifteenth Amendments abolished slavery and extended formal citizenship and voting rights, although racial segregation persisted for nearly a century.

Industrialisation, mass immigration, and continental settlement transformed the country in the late nineteenth and early twentieth centuries. The United States entered the First World War in 1917 and emerged from the Second World War in 1945 as one of two global superpowers, anchoring the Western alliance through NATO from 1949 and competing with the Soviet Union throughout the Cold War. Domestically, the New Deal of the 1930s expanded the federal government's economic role, and the civil rights movement of the 1950s and 1960s produced landmark legislation, notably the Civil Rights Act of 1964 and the Voting Rights Act of 1965, dismantling legal segregation.

After the Cold War ended in 1991, the United States operated as the world's preeminent military and economic power, leading interventions in the Gulf, the Balkans, Afghanistan, and Iraq, the latter two following the attacks of 11 September 2001. The early twenty-first century brought the 2008 financial crisis, sharper political polarisation, and contested presidential transitions, alongside the seating of successive elected administrations.

The United States today is a constitutional federal republic of fifty states, a federal district, and several territories, governed under the 1789 Constitution through an elected president, a bicameral Congress, and an independent federal judiciary, with substantial powers reserved to the states.