commander-in-chief of the expeditionary force against the eastern barbarians
Historical title used from 940 to 1335, specifically for the general leading campaigns against the eastern Emishi or other groups considered barbarians. Compare with 征東将軍, a lower-ranking general in the same context.
See also: 征東将軍
The Seitō Taishōgun was appointed as the supreme commander of eastern expeditions from the Heian period through the Nanboku-chō period.
征東将軍 is a lower-ranking general under the 征東大将軍, or a similar title used in different periods. 征東大将軍 specifically denotes the supreme commander.
Compound of 征東 (seitō, 'subjugation of the east') and 大将軍 (taishōgun, 'great general'). The title was created in the Heian period for campaigns against the Emishi and later used in various eastern military expeditions.