In international law, a war of aggression is generally considered to be any war for which the purpose is not to repel an invasion, or respond to an attack on the territory of a sovereign nation. This definition derives from the just war doctrine and, above all, the United Nations Charter, which provides for the inherent right of individual or collective self-defence if an armed attack occurs. While waging a war of aggression was one of the indictments in the Nuremberg Trials because Germany had ratified the Kellogg-Briand Pact of 1928, many unprovoked wars have been fought since without those responsible facing trials afterwards, regardless of their signature to the pact. Some countries even officially proclaim the doctrine of preventive wars.

Sources

• United Nations Charter