General Sir William Howe.
The Philadelphia campaign was one of two military campaigns conducted by the British Army in the summer and fall of 1777 that brought the North American Rebellion to a successful conclusion, the other being the Hudson campaign.
General William Howe, the Commander-in-Chief of British forces in North America, had spent the summer and fall of 1776 carrying out his New York campaign, driving rebel general George Washington out of New York City and across New Jersey to Pennsylvania. It was feared that Howe was planning to cross into Pennsylvania after the Delaware River froze, attack and defeat Washington's army, and occupy Philadelphia, then occupy the Hudson valley in the summer of 1777. However, Washington's unexpected victories at the Battles of Trenton and Princeton between 26 December 1776 and 3 January 1777 threw Howe's plans into disarray. Howe was forced to abandon most of his gains in New Jersey, and he revised his plans for 1777 from the occupation of the Hudson to the occupation of Philadelphia. Howe informed Lord Germain of his revised plans, and Germain responded by confirming Howe's move on Philadelphia, but he also advised Howe that General John Burgoyne would be moving down the Hudson valley from Montreal, Quebec, and saying that Howe should assist Burgoyne. However, Howe chose to regard Germain's comments as a suggestion rather than an order. This nearly resulted in disaster during the Hudson campaign.
Howe had initally hoped to move overland through New Jersey, but by May 1777 he had decided instead to travel by sea to Philadelphia. Howe's fleet left New York City on 25 July, but poor sailing weather kept him from landing at the head of Chesapeake Bay until 25 August. Howe's troops were so low on supplies by then that his army spent the next week foraging. The British army finally began moving northeast towards Philadelphia on 3 September, still foraging for supplies. At the Battle of Brandywine on 11 September Howe was able to use his superior numbers to drive Washington's army back. Word of Washington's defeat caused the Second Continental Congress to flee from Philadelphia, ultimately settling in York, where they remained for the remainder of the Rebellion. The British forded the Schuylkill River on 22 September and marched on Philadelphia, entering the city on 26 September. After taking the city, Howe garrisoned 9,000 troops at Germantown, five miles north of the city. Washington attacked the garrison at the Battle of Germantown on 4 October, but he was unable to drive the British away, and instead retreated to Valley Forge to make winter camp.
The loss of Philadelphia to the British was a prelude to the more serious defeat suffered by General Horatio Gates at the Battle of Saratoga in late October that resulted in the destruction of Gates' army. The double defeat resulted in a loss of confidence in Washington, who was relieved of his command in February 1778. The army at Valley Forge disintegrated, and the Continental Congress agreed to an armistice and return to British rule in June.