Just after both Retired Emperors Junna and Sage died one after another, Imperial Prince Tsunesada's position as Crown Prince was taken, (the Showa Disturbance) and Imperial succession was unified by Emperor Saga - along Emperor Ninmyo's Imperial line.
しかし、淳和・嵯峨両上皇の相次ぐ崩御の直後、恒貞を廃太子（皇太子を廃すること）とする事件（承和の変）が起こり、皇位継承は嵯峨－仁明の系統に統一されることとなった。