Debellatio
The term debellatio or "debellation" (Latin 'defeating, or the act of conquering or subduing', literally, 'warring (the enemy) down', from Latin bellum 'war') describes a situation in which an interstate war ends not with a peace treaty nor a ceasefire, but with the catastrophic state collapse of the losing party as a result of comprehensive military defeat, typically resulting in the disintegration of the institutions capable of issuing an authoritative instrument of surrender.
Israeli law professor Eyal Benvenisti defines debellatio as "a situation in which a party to a conflict has been totally defeated in war, its national institutions have disintegrated, and none of its allies continue to challenge the enemy militarily on its behalf."