Yet at last a happy combination of circumstances enabled the American and French forces, for the first time operating in complete accord, to bring this disastrous war to a most successful conclusion. Well aware of the importance of the Southern campaign, Washington had procured for Greene, the ablest of his generals, command of the forces which were gathering in North Carolina to resist the advance of Cornwallis in 1781. Defeated at the Cowpens and checked at Guilford, the British commander was forced to retire to Wilmington; but instead of returning to Charleston he moved into Virginia to join Arnold, convinced that the conquest of the Old Dominion must precede that of North Carolina. In May and June he carried ruin to all the prosperous towns of the province; but in July, when the American forces under Lafayette had been greatly strengthened, it was no longer safe for the British commander to divide his army. Acting under orders from Clinton, Cornwallis accordingly retired to the coast and fortified the neck of land at Yorktown. Washington had scarcely been apprised of this circumstance before he received a letter from the Count de Grasse, commander of the French naval forces in the West Indies, proposing joint operations in Virginia during the summer, and promising to bring his fleet to the Chesapeake sometime in August. The opportunity was a rare one. Abandoning the projected attack on New York, Washington and Rochambeau joined their forces and marched rapidly through New Jersey, entering Philadelphia the very day that De Grasse appeared at the mouth of the bay. They had already joined Lafayette before Admiral Graves arrived from New York with a British fleet to rescue the British general. Had Graves been a Rodney or a Nelson he might have given a different issue to the American Revolution; but he was not the man to win against great odds, and after an indecisive engagement he sailed away, leaving Cornwallis to his fate. Hemmed in by 16,000 American and French troops, the unhappy general, who never met Washington but to be defeated, surrendered his army of 7000, men on the 19th of October, 1781.