The Shonai district received high economic benefits based on its inclusion of the Shonai plains and Sakata Minato port, so various clans including Uesugi, Mogami and Onodera watched for an opportunity to plunder this area.
またこの地域は庄内平野や酒田市湊を抱えており経済的価値が高く、周囲の上杉氏や最上氏、小野寺氏などが獲得を狙っていた。