French Alliance with America
When fighting started in America the French could not risk an open alliance with the colonists until they were sure the latter were really seeking independence and were capable of a sustained fight to win it. Otherwise the French might find themselves at war with a Britain no longer engaged in America. The advisers of Louis XVI believed that he would do best by letting England wear herself down in a trans-Atlantic war; meanwhile they would keep themselves informed of the situation in the colonies and would send the rebels secret aid. In March of 1776 Silas Deane was sent as an American agent to Paris, and two months later Hortalez and Cie was in business. "Washington's victory at Trenton and Princeton was, perhaps, made possible by the supplies furnished by the French through their instigation," writes Van Tyne, and although Saratoga was the decisive event that brought the French into open alliance, "nine-tenths of the military supplies that made that victory at Saratoga possible came from France or foreign merchants whom she secretly encouraged".
On 17DEC1777, having learned of the victory at Saratoga, French authorities told American envoys in Paris that France had decided to recognize American independence. On 08JAN1778, Vergennes informed the envoys that France was ready to make an alliance. On 4MAY78, Congress ratified two treaties: a treaty of amity and commerce (recognizing independence), and a treaty of alliance to become effective in the event of war between France and England.
France's motive in making the treaty with America was the abasement of England by helping America win independence: she was not in the war for any significant increase of her overseas possessions. As a consequence of the French involvement in the war, the British government decided to abandon Philadelphia and concentrate their main army at New York. The British felt that the post in NY was less susceptible to French naval attack and American offenses. Further, if Clinton's forces in Philadelphia ever found themselves in need of reinforcements, the reinforcements would come from NY. It was understood by the British that the naval force from France, commanded by D'Estaing, would be in position to cut the reinforcements off, leaving Clinton stranded.