In December 1837, Jesup began a massive offensive, culminating in the Battle of Lake Okeechobee, and the war entered a new phase of attrition. During this time, the government realized that it would be almost impossible to drive the remaining Seminoles from Florida, so Van Buren sent General Alexander Macomb to negotiate peace with them. It was the only time that an Indian tribe had forced the government to sue for peace. An agreement was reached allowing the Seminoles to remain in southwest Florida, but the peace was shattered in July 1839 and was not restored until 1842, after Van Buren had left office.