On January 17, 1781, Morgan won a brilliant victory at Cowpens, S.C., which seriously embarrassed Cornwallis; and then succeeded a vigorous campaign between Cornwallis and Greene for several months, over the Carolinas and the borders of Virginia. The losses of the British were so great, even when they had the advantage, that Cornwallis turned his face to the North, with a view of transferring the seat of war to Chesapeake Bay. Washington then sent all the troops he could spare to Virginia, under La Fayette. He was further aided by the French fleet, under De Grasse, whom he persuaded to sail to the Chesapeake. La Fayette here did good service, following closely the retreating army. Clinton failed to reinforce Cornwallis, some say from jealousy, so that the latter felt obliged to fortify himself at Yorktown. Washington, who had been planning an attack on New York, now continued his apparent preparations, to deceive Clinton, but crossed the Hudson on the 23d of August, to co-operate with the French fleet and three thousand French troops in Virginia, to support La Fayette. He rapidly moved his available force by swift marches across New Jersey to Elkton, Maryland, at the head of Chesapeake Bay. The Northern troops were brought down the Chesapeake in transports, gathered by great exertions, and on September 28 landed at Williamsburg, on the Yorktown Peninsula. Cornwallis was now hemmed in by the combined French and American armies. Had he possessed the control of the sea he might have escaped, but as the fleet commanded the Chesapeake this was impossible. He had well fortified himself, however, and on the 5th of October the siege of Yorktown began, followed on the 14th by an assault. On the 19th of October, 1781, Cornwallis was compelled to surrender, with seven thousand troops. The besieging army numbered about five thousand French and eleven thousand Americans. The success of Washington was owing to the rapidity of his movements, and the influence which, with La Fayette, he brought to bear for the retention at this critical time and place of the fleet of the Count de Grasse, who was disposed to sail to the West Indies, as D'Estaing had done the year before. Washington's keen perception of the military situation, energetic promptness of action, and his diplomatic tact and address in this whole affair were remarkable. The surrender of Cornwallis virtually closed the war. The swift concentration of forces from North and South was due to Washington's foresight and splendid energy, while its success was mainly due to the French, without whose aid the campaign could not have been concluded.