The Law of War principle of "military necessity" justifies actions that are:

The principle of "military necessity" within the Law of War is fundamental to understanding the lawful conduct of armed forces during conflict. It justifies measures that are necessary to achieve a legitimate military objective, specifically actions that are indispensable for securing the complete submission of the enemy. This means that any operational decision made by military leaders must directly contribute to the end goal of the military operation, which often involves overcoming the enemy’s capacity to wage war.

The concept is rooted in the need to balance military objectives with humanitarian considerations. While actions taken under the principle of military necessity can be aggressive or destructive, they are deemed legitimate as long as they are aimed at achieving a definitive and lawful military outcome. The overarching intent is to procure a swift conclusion to hostilities and minimize prolonged conflict, which can lead to greater suffering and destruction.

Within this framework, actions that are excessively barbaric or not directed towards a legitimate military aim would not fall under this principle. That creates a boundary whereby even necessity cannot justify actions that are clearly prohibited by international law or that do not assist in achieving a military objective.