The Confederation period was the era of the United States' history in the 1780s after the American Revolution and prior to the ratification of the United States Constitution. In 1781, the United States ratified the Articles of Confederation and Perpetual Union and prevailed in the Battle of Yorktown, the last major land battle between British and American Continental forces in the American Revolutionary War. American independence was confirmed with the 1783 signing of the Treaty of Paris. The fledgling United States faced several challenges, many of which stemmed from the lack of an effective central government and unified political culture. The period ended in 1789 following the ratification of the United States Constitution, which established a new, more effective, federal government.

The Articles of Confederation established a loose confederation of states with a weak confederated government. An assembly of delegates acted on behalf of the states they represented. This unicameral body, officially referred to as the United States in Congress Assembled, had little authority, and could not accomplish anything independent of the states. It had no chief executive, and no court system. Congress lacked the power to levy taxes, regulate foreign or interstate commerce, or effectively negotiate with foreign powers. The weakness of Congress proved self-reinforcing, as the leading political figures of the day served in state governments or foreign posts. The failure of the confederated government to handle the challenges facing the United States led to calls for reform and frequent talk of secession.

The Treaty of Paris left the United States with a vast territory spanning from the Atlantic Ocean to the Mississippi River. Settlement of the trans-Appalachian territories proved difficult, in part due to the resistance of Native Americans and the neighboring foreign powers of Great Britain and Spain. The British refused to evacuate US territory, while the Spanish used their control of the Mississippi River to stymie Western settlement. In 1787, Congress passed the Northwest Ordinance, which set an important precedent by establishing the first organized territory under the control of the confederated government.

After Congressional efforts to amend the Articles failed, numerous American leaders met in Philadelphia in 1787 to establish a new constitution. The new constitution was ratified in 1788, and the new federal government began meeting in 1789, marking the end of the Confederation period.

The American Revolutionary War broke out against British rule in April 1775 with the Battles of Lexington and Concord. The Second Continental Congress met in May 1775, and established an army funded by Congress and under the leadership of George Washington, a Virginian who had fought in the French and Indian War. On July 4, 1776, as the war continued and two days after endorsing the Lee Resolution to break from British control, Congress adopted the Declaration of Independence. At exactly the same time that Congress declared independence, it also created a committee to craft a constitution for the new nation. Though some in Congress hoped for a strong centralized state, most Americans wanted legislative power to rest primarily with the states and saw the central government as a mere wartime necessity. The resulting constitution, which came to be known as the Articles of Confederation and Perpetual Union, provided for a weak central government with little power to coerce the state governments. The first article of the new constitution established a name for the new federation – the United States of America.

The first draft of the Articles of Confederation, written by John Dickinson, was presented to Congress on July 12, 1776, but Congress did not send the proposed constitution to the states until November 1777. Three major constitutional issues divided Congress: state borders, including claims to lands west of the Appalachian Mountains, state representation in the new Congress, and whether tax levies on states should take slaves into account. Ultimately, Congress decided that each state would have one vote in Congress and that slaves would not affect state levies. By 1780, as the war continued, every state but Maryland had ratified the Articles; Maryland refused to ratify the constitution until all of the other states relinquished their western land claims to Congress. The success of Britain's Southern strategy, along with pressure from America's French allies, convinced Virginia to cede its claims north of the Ohio River, and Maryland finally ratified the Articles in January 1781. The new constitution took effect in March 1781 and the Congress of the Confederation technically replaced the Second Continental Congress as the central government, but in practice the structure and personnel of the new Congress was quite similar to that of the old Congress.

After the American victory at the Battle of Yorktown in September 1781 and the collapse of British Prime Minister North's ministry in March 1782, both sides sought a peace agreement. The American Revolutionary War ended with the signing of the 1783 Treaty of Paris. The treaty granted the United States independence, as well as control of a vast region south of the Great Lakes and extending from the Appalachian Mountains west to the Mississippi River. Although the British Parliament had attached this trans-Appalachian region to Quebec in 1774 as part of the Quebec Act, several states had land claims in region based on royal charters and proclamations that defined their boundaries as stretching "from sea to sea." Some Americans had hoped the treaty would provide for the acquisition of Florida, but that territory was restored to Spain, which had joined the U.S. and France in the war against Britain and demanded its spoils. The British fought hard and successfully to keep Canada, so the treaty acknowledged that.

Observers at the time and historians ever since emphasize the generosity of British territorial concessions. Historians such as Alvord, Harlow, and Ritcheson have emphasized that Britain's generous territorial terms were based on a statesmanlike vision of close economic ties between Britain and the United States. The treaty was designed to facilitate the growth of the American population and create lucrative markets for British merchants, without any military or administrative costs to Britain. As the French foreign minister Vergennes later put it, "The English buy peace rather than make it".