When the United Nations (UN) Charter was adopted, it was generally considered to have outlawed war. States accepted the obligation to settle all disputes by peaceful means and to refrain from the use or threat of use of force in their international relations. Only two exceptions were expressly allowed: force used in self-defense when an armed attack occurs, and armed action authorized by the UN Security Council as an enforcement measure. These provisions were seen by most observers as the heart of the Charter. and the most important principles of contemporary international law. They have been reaffirmed over and over again in unanimous declarations of the United Nations, in treaties and in statements of political leaders.
The Right of States to Use Armed Force,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol82/iss5/32