The Philadelphia campaign (1777–1778) was a British initiative in the American Revolutionary War. The campaign was controversial because, although British General William Howe successfully captured the revolutionary capital of Philadelphia, he proceeded slowly and did not aid the concurrent Saratoga campaign further north, which ended in disaster for the British. General Howe resigned during the occupation of Philadelphia and was replaced by his second-in-command, General Sir Henry Clinton, who evacuated Philadelphia in order to reinforce New York City.

Capture of Philadelphia

Having secured New York City in his 1776 campaign, in 1777 General Howe concentrated on capturing Philadelphia, the seat of the Revolutionary government. He moved slowly, landing 15,000 troops in late August at the northern end of Chesapeake Bay, about 55 miles (90 km) southwest of Philadelphia. General George Washington positioned 11,000 men between Howe and Philadelphia but was outflanked and driven back at the Battle of Brandywine on September 11, 1777.

The Continental Congress once again abandoned the city, hastening to Lancaster, Pennsylvania, and later York, Pennsylvania. British and Revolutionary forces maneuvered around each other for the next several days, clashing in minor encounters such as the so-called "Paoli Massacre." On September 26, Howe finally outmaneuvered Washington and marched into Philadelphia unopposed. But it did not bring the end to the "rebellion" as the British thought it would. In 18th century warfare, normally the side that captured the other side's capital city won the war. But the war was to continue for six more years (until 1783).

After taking the city, the British garrisoned about 9,000 troops in Germantown, five miles (8 km) north of Philadelphia. Washington unsuccessfully attacked Germantown on October 4, and then retreated to watch and wait. Meanwhile, the British secured the Delaware River by taking forts Mifflin and Mercer in November. In early December, Washington successfully repelled a British attack at the Battle of White Marsh.

General Washington's problems at this time were not just with the British. In the so-called Conway Cabal, some politicians and officers unhappy with Washington's recent performance as commander-in-chief secretively discussed his removal. Washington, offended by the behind-the-scenes maneuvering, laid the whole matter openly before Congress. His supporters rallied behind him, and the episode was abated.

Valley Forge and Monmouth

Washington and his army encamped at Valley Forge in December 1777, about 20 miles (32 km) from Philadelphia, where they stayed for the next six months. Over the winter, 2,500 men (out of 10,000) died from disease and exposure. However, the army eventually emerged from Valley Forge in good order, thanks in part to a training program supervised by Baron von Steuben.

Meanwhile, there was a shakeup in the British command, with Sir Henry Clinton replacing Howe, who had resigned, as commander-in-chief. France's entry into the war had changed British war strategy, and Clinton was ordered by the government to abandon Philadelphia and defend New York City, now vulnerable to French naval power.
Washington sent out Lafayette with an advanced guard, which the British ambushed at the Battle of Barren Hill.

Washington's army shadowed Clinton on his withdrawal and forced a battle at Monmouth on June 28, 1778, the last major battle in the North. Washington's second-in-command, General Charles Lee, ordered a controversial retreat during the battle, allowing Clinton's army to escape. By July, Clinton was in New York City, and Washington was again at White Plains, New York. Both armies were back where they had been two years earlier. With the exception of scattered minor actions in the North, like the Battle of Stony Point, the focus of the war shifted elsewhere.