"The League of Nations? Surely nations knew laws other than warfare? What of diplomacy? "

The League of Nations was established after the Treaty of Versailles and had its largest membership of 58 countries in the mid 1930s. It aimed to prevent war or indeed other forms of international conflict by acting as an arbiter. In rare cases it would enforce its resolutions by exercising military power or else imposing economic sanctions. It sought also to promote global health and human rights, improve working conditions as well as bring about multilateral disarmament.  Dictators Mussolini and Hitler refused to bow to the League of Nations' call for universal equality, claiming that some minority groups were subhuman and therefore ineligible for protection under human rights laws. Though it was successful in some respects, it was of course unable to defuse the time bomb that was Nazi Germany. Today many successful global organizations as well as the United Nations find their root in the League of Nations.