Iwase Province was created during the reign of Empress Genshō. The Yōrō Ritsuryo established the Iwase Province in 718 through the division of the Michinoku Province (Mutsu Province). It was composed of five districts of Shirakawa (白河), Iwase (石背), Aizu (会津), Asaka (安積) and Shinobu (信夫).
The area encompassed by the province reverted to Mutsu some time between 722 and 724. Some scholars have suggested that this innovation may have been motivated by economic considerations.
- Aizu District (会津郡)
- Asaka District (安積郡)
- Iwase District (岩瀬郡)
- Shinobu District (信夫郡)
- Shirakawa District (白川郡, East Shirakawa)
- Kodama. (1958). 図日本文化史大系, p. 30; excerpt, 石背国 718-724?
- Meyners d'Estrey, Guillaume Henry Jean (1884). Annales de l'Extrême Orient et de l'Afrique, Vol. 6, p. 172, p. 172, at Google Books; excerpt, Genshō crée sept provinces : Idzumi, Noto, Atoa, Iwaki, Iwase, Suwa et Sado en empiétant sur celles de Kawachi, Echizen, Etchū, Kazusa, Mutsu and Shinano
- Kodama. (1958). 図日本文化史大系 (Zusetsu Nihon bunkashi taikei). Tokyo: Shōgakkan. OCLC 16308019
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