Who were the wakou/wokou who raided the coastline of China, Japan, and Korea? Were they Japaneses, or Koreans? Where did they come from; were they former sailors? Fishermen who turned into sea banditry? What were their lifestyle? Were there any major trades that got disrupted by their presence?
The wokou were originally Japanese, hence the name (wo means Japanese, kou means thief/pirate). However, at the height of the wokou crisis of the 16th century, most of the pirates were ethnic Chinese. In 1550, the Ming dynasty government instituted the haijin, or "sea ban", which outlawed all private maritime trade, supposedly to starve out the pirates. However, this had the opposite effect. The Chinese merchants who no longer had a livelihood turned to smuggling and piracy in order to survive. The 16th century wokou banded together in large fleets and sometimes launched large-scale attacks on coastal towns. They also sometimes had the support of corrupt government officials, who were called "pirates in cap and gown". The pirate attacks dropped off after the re-legalization of maritime trade in 1567.
Source: Autarky and the Rise and Fall of Piracy in Ming China
Edit: Another good source if you can find a copy is "From haijin to kaihai: The Jiajing Court's search for a modus operandi along the southeastern coast (1522 - 1567)" by Ivy Lim.