Striking at an enemy before they can strike against you is known as ”pre-emptive self-defense” and traditionally two conditions, known as the “Caroline test” need to be fulfilled to justify such an action.

The "Caroline" was an American steamboat used to supply settlers rebelling against the British Colonial government in Canada in 1837. American sympathizers provided weapons and food to the rebels, effectively keeping them in a fight they would otherwise lose.

The British decided that enough was enough and a force entered the United States during the night, set the boat ablaze and spectacularly sent it over the Niagara Falls. One American was killed in the operation.

The British argued that this was simply self-defense because

It has since become accepted as part of customary international law and was for example cited at the Nuremberg Tribunal.

Campaign: “Curse of Strahd”, Dungeons & Dragons

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