When the American Revolutionary War broke out in 1775, Charles William Ferdinand saw an opportunity to replenish the state's treasury by renting its well-trained army to Great Britain. In 1776, Charles I signed a treaty supporting Britain in the war, the first prince to do so. Under the terms of this treaty, Brunswick-Wolfenbüttel supplied 4,000 troops for service with the British armies in America, under the command of general Friedrich Adolf Riedesel. Riedesel was given command of all the German troops serving in the Saratoga campaign, under British general John Burgoyne. Burgoyne was defeated in the Battles of Saratoga (1777), and his troops were taken captive as the Convention Army. Although the terms of surrender allowed the Convention Army to give their parole and return to Europe, the American Continental Congress revoked the convention. The Convention Army was kept in captivity until the war ended in 1783.