It was the capture of Burgoyne at Saratoga which brought decision to France. That was the victory which Vergennes had demanded before he would take open action. One British army had surrendered. Another was in an untenable position in Philadelphia. It was known that the British fleet had declined. With the best of it in America, France was the more likely to win successes in Europe. The Bourbon king of France could, too, draw into the war the Bourbon king of Spain, and Spain had good ships. The defects of France and Spain on the sea were not in ships but in men. The invasion of England was not improbable and then less than a score of years might give France both avenging justice for her recent humiliation and safety for her future. Britain should lose America, she should lose India, she should pay in a hundred ways for her past triumphs, for the arrogance of Pitt, who had declared that he would so reduce France that she should never again rise. The future should belong not to Britain but to France. Thus it was that fervent patriotism argued after the defeat of Burgoyne. Frederick the Great told his ambassador at Paris to urge upon France that she had now a chance to strike England which might never again come. France need not, he said, fear his enmity, for he was as likely to help England as the devil to help a Christian. Whatever doubts Vergennes may have entertained about an open alliance with America were now swept away. The treaty of friendship with America was signed on February 6, 1778. On the 13th of March the French ambassador in London told the British Government, with studied insolence of tone, that the United States were by their own declaration independent. Only a few weeks earlier the British ministry had said that there was no prospect of any foreign intervention to help the Americans and now in the most galling manner France told George III the one thing to which he would not listen, that a great part of his sovereignty was gone. Each country withdrew its ambassador and war quickly followed.