Total war is sometimes used to mean the mobilization of all resources, economic and military, by a society in support of a war effort; this was the American description of its own engagement during World War II. It has also been used to mean a willingness to engage the enemy in any geographic zone, or with any available weaponry, or sometimes a willingness to fight a scorched-earth campaign, even on one’s own territory. It has also been used to mean war conducted against an enemy’s military and economic infrastructure, across all of its territory, in order to cripple the enemy’s ability to wage war; Great Britain used the term in this sense in both World Wars. The term has also been used to mean a willingness to countenance any method or means of warfare, legal or illegal, including, for example, weapons categorically considered illegal, such as chemical or biological weapons. These extremely varied uses of the term total war have radically different legal implications within international humanitarian law (IHL).

The first three meanings of total war need not imply violations of IHL. It is possible, for example, under IHL to mobilize all of a society’s resources to war ends. It is also possible to fight lawfully within IHL in any theater or with any legal weapons. It is even possible, although more difficult, to fight a war attacking military-economic infrastructure legally, provided that the attacking forces respect IHL rules regarding indiscriminate attack. Where a party to conflict runs afoul of IHL is the belief that total war permits the suspension of the laws of armed conflict.

IHL applies however intense the armed conflict. Any State that attempted to fight a total war, in the sense that it declared it would not abide by the limitations imposed on its conduct of the conflict by IHL, would be in violation of IHL and presumably would find itself the subject of UN Security Council resolutions.

In addition, it is no defense to individual or State liability for breaches of IHL that one's enemy is fighting a total war. Nor is it a defense to plead military necessity; military necessity only justifies actions that are themselves legal. IHL itself gives some latitude to commanders to conduct military operations, but they must act within the limitations of IHL. Nor is it a defense to argue that your breaches of IHL, as part of a total war, are in reprisal for the acts of your enemy. There are specific prohibitions in the Geneva Conventions of 1949 and in the 1977 Additional Protocol I of reprisals against those protected by these instruments, such as the civilian population, civilian objects, the wounded and sick, and prisoners of war.

(See legitimate military targets; limited war; military objectives.)