It was extremely difficult for Washington to convert his "Continentals" into an efficient fighting force. They were short of money and supplies, and lacked training and discipline. However, the task was not much easier for the British. Although, as in the war against France twenty years earlier, the British Navy could control the Atlantic and block any ships sailing to the Americans' assistance, it was difficult to put a regular British army into the field to fight. Officers were poorly trained and had often obtained their commissions because of family or political connections, rather than through merit. In the end, 18000 German mercenaries from Hesse had to be hired to assist in the fighting.

The British strategy was to split the colonies geographically into two by sending armies south from Canada, down the Hudson River, and north from New York, up the same river. Movement could only take place in Spring and Summer, which slowed the whole process down for years. In October 1777, a British army was trapped at Saratoga, New York, and surrounded, outnumbered and, with no hope of rescue, was forced to surrender.

This defeat shook the British Empire. France, which had secretly been helping the Americans anyway, now signed a Treaty (February 1778) and prepared to send men and ships to the Americans' assistance. Spain and Holland also went to war against Britain.

In October 1781, a second British army was trapped at Yorktown, Virginia. In front of it were 16000 American soldiers under Washington, and to its rear a French fleet. "I nearly think this Empire is ruined," said George III on hearing of the defeat.

It was now only a matter of time before Britain got out of the war as best it could, leaving the colonies their independence. In 1783, at the Peace of Versailles, the colonies' independence was recognised and small colonial gains were given to France and Spain.