EIGHTY-SIX YEARS AGO THE MAJOR POWERS BANNED WAR
The Kellogg-Briand pact was signed on this day in 1928 declaring:
Deeply sensible of their solemn duty to promote the welfare of mankind;
Persuaded that the time has, come when a frank renunciation of war as an instrument of na tional policy should be made to the end that the peaceful and friendly relations now existing between their peoples may be perpetuated;
Convinced that all changes in their relations with one another should be sought only by pacific means and be the result of a peaceful and orderly process, and that any signatory Power which shall hereafter seek to promote its ts national interests by resort to war a should be denied the benefits furnished by this Treaty;
Hopeful that, encouraged by their example, all the other nations of the world will join in this humane endeavor and by adhering to the present Treaty as soon as it comes into force bring their peoples within the scope of its beneficent provisions, thus uniting the civilized nations of the world in a common renunciation of war as an instrument of their national policy.
The treaty was ratified by the U.S. and 61 other countries in total, although it clearly did little to stop a second world war a little over a decade later.
It may not have been a total failure, however, as explained in Wikipedia:
As a practical matter, the Kellogg–Briand Pact did not live up to its aim of ending war, and in this sense it made no immediate contribution to international peace and proved to be ineffective in the years to come. Moreover, the pact erased the legal distinction between war and peace because the signatories, having renounced the use of war, began to wage wars without declaring them as in the Japanese invasion of Manchuria in 1931, the Italian invasion of Abyssinia in 1935, the Soviet invasion of Finland in 1939, the German and Soviet Union invasions of Poland.
Nevertheless, the pact is an important multilateral treaty because, in addition to binding the particular nations that signed it, it has also served as one of the legal bases establishing the international norms that the threat or use of military force in contravention of international law, as well as the territorial acquisitions resulting from it, are unlawful.
Notably, the pact served as the legal basis for the creation of the notion of crime against peace – it was for committing this crime that the Nuremberg Tribunal and Tokyo Tribunal sentenced a number of people responsible for starting World War II.