American Revolutionary War: British troops abandon Philadelphia.

Philadelphia is a major city in the Commonwealth of Pennsylvania in the United States. With a population of 1,603,797 as of 2020, Philadelphia is Pennsylvania's most populous city, the sixth most populous city in the U.S., and the second most populous city on the U.S. East Coast, behind New York City. Since 1854, the city has had the same geographic boundaries as Philadelphia County, the most populous county in Pennsylvania and the urban core of the Delaware Valley, the nation's seventh largest and world's 35th largest metropolitan region with 6.096 million residents as of 2020.Philadelphia was founded in 1682 by William Penn, an English Quaker. The city served as capital of the Pennsylvania Colony during the British colonial era. Philadelphia went on to play a historic and vital role in the 18th century as the central meeting place for the nation's founding fathers whose plans and actions in Philadelphia ultimately inspired and resulted in the American Revolution. Philadelphia hosted the First Continental Congress in 1774 following the Boston Tea Party, preserved the Liberty Bell, and hosted the Second Continental Congress during which the founders signed the Declaration of Independence, which historian Joseph Ellis has described as "the most potent and consequential words in American history." Once the Revolutionary War commenced, both the Battle of Germantown and the Siege of Fort Mifflin were fought within Philadelphia's city limits.

The U.S. Constitution was later ratified in Philadelphia at the Philadelphia Convention of 1787. Philadelphia remained the nation's largest city until 1790, when it was surpassed by New York City, and served as the nation's first capital from May 10, 1775 until December 12, 1776 and on four subsequent occasions during and following the American Revolution, including from 1790 to 1800 while the new national capital of Washington, D.C. was under construction.

In the 19th and 20th centuries, Philadelphia became a major national industrial center and railroad hub. Its industrial jobs attracted European immigrants, most of whom initially came from Ireland and Germany, the two largest reported ancestry groups in the city as of 2015. Later immigrant groups in the 20th century came from Italy (Italian being the third-largest European ethnic ancestry currently reported in Philadelphia) and other Southern European and Eastern European countries. In the early 20th century, Philadelphia became a prime destination for African Americans during the Great Migration after the Civil War. Puerto Ricans began moving to the city in large numbers in the period between World War I and II, and in even greater numbers in the post-war period. The city's population doubled from one million to two million people between 1890 and 1950.

The Philadelphia area's many universities and colleges make it a top national center for education and academic research. As of 2019, the Philadelphia metropolitan area is estimated to produce a gross metropolitan product (GMP) of $490 billion. Philadelphia is the center of economic activity in Pennsylvania and is home to five Fortune 1000 companies. The Philadelphia skyline is expanding, with a market of almost 81,900 commercial properties in 2016, including several nationally prominent skyscrapers. Philadelphia has more outdoor sculptures and murals than any other American city. Fairmount Park, when combined with the adjacent Wissahickon Valley Park in the same watershed, is one of the largest contiguous urban park areas in the United States. The city is known for its arts, culture, cuisine, and colonial history, attracting 42 million domestic tourists in 2016 who spent $6.8 billion, generating an estimated $11 billion in total economic impact in the city and surrounding four counties of Pennsylvania. Philadelphia is also a biotechnology hub.Philadelphia is the home of many U.S. firsts, including the nation's first library (1731), hospital (1751), medical school (1765), national capital (1774), university (by some accounts) (1779), stock exchange (1790), zoo (1874), and business school (1881). Philadelphia contains 67 National Historic Landmarks, including the World Heritage Site of Independence Hall. In 2015, Philadelphia was the first U.S. city to be named to the Organization of World Heritage Cities.

The American Revolutionary War (April 19, 1775 – September 3, 1783), also known as the Revolutionary War or American War of Independence, secured a United States of America independent from Great Britain. Fighting began on April 19, 1775, followed by the Declaration of Independence on July 4, 1776. The American Patriots were supported by France and Spain, conflict taking place in North America, the Caribbean, and Atlantic Ocean. It ended on September 3, 1783 when Britain accepted American independence in the Treaty of Paris, while the Treaties of Versailles resolved separate conflicts with France and Spain.Established by Royal charter in the 17th and 18th centuries, the American colonies were largely autonomous in domestic affairs and commercially prosperous, trading with Britain and its Caribbean colonies, as well as other European powers via their Caribbean entrepôts. After British victory in the Seven Years' War in 1763, tensions arose over trade, colonial policy in the Northwest Territory and taxation measures, including the Stamp Act and Townshend Acts. Colonial opposition led to the 1770 Boston Massacre and 1773 Boston Tea Party, with Parliament responding by imposing the so-called Intolerable Acts.

On September 5, 1774, the First Continental Congress drafted a Petition to the King and organized a boycott of British goods. Despite attempts to achieve a peaceful solution, fighting began with the Battle of Lexington on April 19, 1775 and in June Congress authorized George Washington to create a Continental Army. Although the "coercion policy" advocated by the North ministry was opposed by a faction within Parliament, both sides increasingly viewed conflict as inevitable. The Olive Branch Petition sent by Congress to George III in July 1775 was rejected and in August Parliament declared the colonies to be in a state of rebellion.

Following the loss of Boston in March 1776, Sir William Howe, the new British commander-in-chief, launched the New York and New Jersey campaign. He captured New York City in November, before Washington won small but significant victories at Trenton and Princeton, which restored Patriot confidence. In summer 1777, Howe succeeded in taking Philadelphia, but in October a separate force under John Burgoyne was forced to surrender at Saratoga. This victory was crucial in convincing powers like France and Spain an independent United States was a viable entity.

France provided the US informal economic and military support from the beginning of the rebellion, and after Saratoga the two countries signed a commercial agreement and a Treaty of Alliance in February 1778. In return for a guarantee of independence, Congress joined France in its global war with Britain and agreed to defend the French West Indies. Spain also allied with France against Britain in the Treaty of Aranjuez (1779), though it did not formally ally with the Americans. Nevertheless, access to ports in Spanish Louisiana allowed the Patriots to import arms and supplies, while the Spanish Gulf Coast campaign deprived the Royal Navy of key bases in the south.

This undermined the 1778 strategy devised by Howe's replacement, Sir Henry Clinton, which took the war into the Southern United States. Despite some initial success, by September 1781 Cornwallis was besieged by a Franco-American force in Yorktown. After an attempt to resupply the garrison failed, Cornwallis surrendered in October, and although the British wars with France and Spain continued for another two years, this ended fighting in North America. In April 1782, the North ministry was replaced by a new British government which accepted American independence and began negotiating the Treaty of Paris, ratified on September 3, 1783.