During the Punitive Expedition into Mexico in 1916-1917, Mexicans generally refused to help American troops, who they viewed as invaders. But Chinese workers in Mexico did assist, working in various capacities, selling goods and services, etc. When the U.S. forces pulled out, the Chinese were in danger of persecution. So General John Pershing asked federal officials to allow them to immigrate to the U.S. The Chinese Exclusion Law forbade that—but the government made an exception, and more than 400 Chinese entered the U.S. Most became citizens within a few years.