In 1919, countries decided to sign the Covenant of the League of Nations, which did not actually prohibit war but established a procedure for settling disputes between countries in a peaceful manner, to avoid war.
The High Contracting Parties,
In order to promote international cooperation and to achieve international peace and security
- By the acceptance of obligations not to resort to war
- By the prescription of open, just and honourable relations between nations
- By the firm establishment of the understandings of international law as the actual rule of conduct among Governments
- By the maintenance of justice and a scrupulous respect for all treaty obligations in the dealings of organized peoples with one another
Agree to this Covenant of the League of Nations.
Any war or threat of war (…) is hereby declared a matter of concern to the whole League, and the League shall take any action that may be deemed wise and effectual to safeguard the peace of nations.
The Members of the League agree that, if there should arise between them any dispute likely to lead to a rupture they will submit the matter either to arbitration or judicial settlement or to enquiry by the Council, and they agree in no case to resort to war until three months after the award by the arbitrators or the judicial decision, or the report by the Council…
…If a report by the Council is unanimously agreed to by the members thereof, the Members of the League agree that they will not go to war with any party to the dispute which complies with the recommendations of the report. If the Council fails to reach a report which is unanimously agreed to by the members thereof, the Members of the League reserve to themselves the right to take such action as they shall consider necessary for the maintenance of right and justice…
In the last 3,421 years of recorded history only 268 have seen no war.
– Will and Ariel Durant, The Lessons of History