 Work on Hirosaki Castle was completed in 1611, replacing Horikoshi Castle as the Tsugaru clan's fortress.By 1631, the Tsugaru clan had solidified their control over their gains made during the Sengoku period.In 1868 Mutsu Province was broken up into five provinces in the aftermath of the Boshin War, with its namesake province, Rikuō occupying what would later become Aomori Prefecture and the northwestern corner of Iwate Prefecture.