Why did the Hongwu emperor’s missions to Japan fail to stop coastal piracy?

The Hongwu emperor’s diplomatic missions to Japan failed to curb coastal piracy primarily because the Japanese authorities were themselves helpless to control the marauders.1

During this period, Japan was experiencing internal disturbances, and the central government lacked the power to suppress the pirate groups, known as wakō, who raided the Chinese and Korean coasts. Although the Hongwu emperor sent three missions to Japan armed with both inducements and threats, these efforts were ineffective because the Japanese leadership could not enforce order over the decentralized feudal groups and pirates operating from the maritime districts.123

Ultimately, the Hongwu emperor addressed the threat not through these failed diplomatic missions, but by constructing strong fortresses and coastal defense fleets to repel the marauders directly.4