using foreigners to control foreigners; playing one barbarian state against another
A classical Chinese strategy of employing one foreign or barbarian group to subdue another. In Japanese, it appears mainly in discussions of historical East Asian diplomacy or military tactics. The synonymous expression 夷を以て夷を制す is more common.
See also: 夷を以て夷を制す
'以夷攻夷' is known as one of the traditional Chinese diplomatic strategies.
From Classical Chinese 以夷攻夷 (yǐ yí gōng yí), literally 'use barbarians to attack barbarians'. The expression entered Japanese as a Sino-Japanese compound and is used in historical and strategic contexts.