Since Tsushima was considered one of the most important bases of the wako pirates, the So clan, who was the governor of Tsushima Province, was requested to cooperate with the Korean Dynasty, so the So clan responded to that request and eventually began to undertake active participation in the trade between Japan and Korea.
特に対馬は倭寇の一大拠点と目されており、対馬守護であった宗氏に対してもこうした協力が要請され、宗氏もそれに応え日朝交易に積極的に参加をしていった。