France had already been secretly funneling funds and weapons to the American armies during the first two years of the American Revolution. Following the Americans' victory at the Battle of Saratoga in October 1777, King Louis XVIII entered into an alliance with the Americans. France's entry into the war also brought the power of their allies, Spain and Holland, against the British. While French troops and their navy added greatly to the cause in America, all three of America's new allies brought new pressure to Great Britain from the European continent. England was forced to deal with a more global war, since an invasion of the island from the continent was now a real threat. King George suspected that France's alliance with the Americans would cost England a large portion of the colonies, but he hoped to carry on the fight in other theatres, such as Quebec and the West Indies. He hoped the 30,000 troops already in the colonies, along with Loyalist support, would prolong the war until he could deal with the French/Spanish threat in Europe.
French military might greatly aided the Americans. At the Battle of Yorktown, for example, a French army of 8,000 under Comte de Rochambeau joined 29 French warships in eventually forcing the British surrender. Perhaps the most famous Frenchman to join the American cause was the Marquis de Lafayette, who became a trusted advisor to General George Washington.