 After victory in the American Civil War in 1865, the United States made clear that France would have to leave.It sent 50,000 troops under General Philip H. Sheridan to the U.S.-Mexico border and helped resupply Juárez.Napoleon's military was stretched very thin; he had committed 40,000 troops to Mexico, 20,000 to Rome to guard the Pope against the Italians, and another 80,000 in restive Algeria.