Early in the 15th century, the Feudal Joson Dynasty made an expedition into Tsushima for punishing the Japanese pirates who had done predatory acts in Korea and other Asian countries. Then, it showed such kindness as allowing them to reside and conduct trade in the above-said three inlets.

After all, the number of Japanese households residing in those inlets grew from 60 to more than 10000 in the late 15th century.

However, the insolent Japanese pirates indulged in all sorts of illegal acts and plunder and even did an act of aggression in conspiracy with those in Tsushima.

In early April 1510, the Japanese pirates in Tsushima made a surprise attack on Naengipho and Pusanpho by more than 100 ships. They, in collaboration with Japs residing in the three inlets, occupied several castles in the inlets and killed a government official. They also plundered and fired Koreans' property and killed many innocent inhabitants in Koje Island.

The Feudal Joson Dynasty let the local army of Kyongsang Province make counterattack on the Japanese pirates and repel them on April 19. And it took a tough measure to completely cut all relations with Tsushima after shattering their aggression against Korea.

As seen above, the Japanese aggressors are the sworn enemy that had plundered Korea and inflicted untold sufferings on its people from the middle ages.