In 1777, British general John Burgoyne led the Saratoga campaign to gain control of the Hudson River during the American Revolutionary War. He was weakened by loss of time and men after the Battle of Oriskany and was forced to surrender after the Battles of Saratoga in October. News of his surrender prompted France to enter the war as an American ally. The British were concerned that the French might attempt to retake parts of New France which they had lost in the French and Indian War, so they adopted a defensive strategy in Quebec. They recruited Loyalists and enlisted Indian allies to conduct a frontier war along the northern and western borders of the Thirteen Colonies.