In 1555 after Harukata SUE died in the battle of Itsukushima with Motonari MORI, the appeal of Yoshinaga was low because although he was related by blood he was an adopted son whose adoption had been severed once, and the vassals were collapsing because they had been weakened by Harukata SUE's plot and internal strife, and the Ouchi clan subsequently fell into a rapid decline.
弘治元年（1555年）、陶晴賢が毛利元就との厳島合戦で敗死すると、血縁があるとはいえ一度解消された経緯のある養子だった義長の求心力は低く、ただでさえ陶晴賢の謀反やその他の内訌で弱体化していた家臣団は完全に崩壊し、大内氏は急速に衰退していく。