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, named 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 at some point between 722 and 724. Some scholars have suggested that this may have been motivated by economic considerations. == Historical districts ==