After revolts against the much-hated Mongolian rulers, which overthrew the Yuan dynasty, the martial Ming dynasty came to power. The Ming evicted the Mongolians from China and then invaded Mongolia themselves. The military expansion under the Ming not only called for an army, but also for a strong navy. It was used to fight off Japanese pirates who frequently attacked and pillaged Chinese coastal cities. The Japanese especially liked the Chinese copper coins that were valued higher in Japan than in China itself.