Since the Otomo clan had been shugo (military governor) of Bungo Province for a long time, aiming at subjugation of northern Kyushu, it was infuriated with the Ouchi clan -- There had been small-scale to medium-scale power struggles between the Otomo and the Ouchi clans around such regions as Buzen and Chikugo from the fifteenth century to the first half of the sixteenth century.
これは、昔から豊後守護であり、北九州を抑えようとしていた大友氏には忌々しい存在であり、15世紀から16世紀前半には豊前や筑前などを舞台に大友と大内の小中規模な勢力争いが続いていた。