The American Revolution was a political upheaval during the last half of the 18th century in which thirteen colonies in North America joined together to break free from the British Empire, combining to become the United States of America. They first rejected the authority of theParliament of Great Britain to govern them from overseas without representation, and then expelled all royal officials. By 1774, each colony had established a Provincial Congress, or an equivalent governmental institution, to govern itself, but still within the empire. The British responded by sending combat troops to re-impose direct rule. Through the Second Continental Congress, the Americans managed the armed conflict against the British known as the American Revolutionary War (also: American War of Independence, 1775–83).

The British sent invasion armies and used their powerful navy to blockade the coast. George Washington became the American commander, working with Congress and the states to raise armies and neutralize the influence of Loyalists. Claiming the rule of George III of Great Britainwas tyrannical and therefore illegitimate, Congress declared independence as a new nation in July 1776, when Thomas Jefferson wrote and the states unanimously ratified the United States Declaration of Independence. The British lost Boston in 1776, but then captured New York City.

After a British army was captured by the American army at Saratoga, the French balanced naval power by entering the war in 1778 as allies of the United States. A combined American-French force captured a second British army at Yorktown in 1781, effectively ending the war. A peace treaty in 1783 confirmed the new nation's complete separation from the British Empire, and resulted in the United States taking possession of nearly all the territory east of the Mississippi River.

The American Revolution was the result of a series of social, political, and intellectual transformations in early American society and government, collectively referred to as the American Enlightenment. Americans rejected the aristocracies that dominated Europe at the time, championing instead the development of republicanism based on the Enlightenment understanding of liberalism. Among the significant results of the revolution was the creation of a democratically-elected representative government responsible to the will of the people. However, sharp political debates erupted over the appropriate level of democracydesirable in the new government, with a number of Founders fearing mob rule.

Many fundamental issues of national governance were settled with the ratification of the United States Constitution in 1788, which replaced the relatively weaker first attempt at a national government adopted in 1781, the Articles of Confederation and Perpetual Union. In contrast to the loose confederation, the Constitution established a strong federated government. The United States Bill of Rights (1791), comprising the first ten constitutional amendments, quickly followed. It guaranteed many "natural rights" that were influential in justifying the revolution, and attempted to balance a strong national government with relatively broad personal liberties. The American shift to liberal republicanism, and the gradually increasing democracy, caused an upheaval of traditional social hierarchy and gave birth to the ethic that has formed a core of political values in the United States.^[1][2]