The League of Nations was the precursor to the United Nations. It was established in the Paris Peace Conference of 1919, and it was seen as a more civilized way for governments to settle differences or conflicts through negotiation and diplomacy. After WWI, the world saw how destructive the new technology of war can absolutely decimate countries and take millions of lives. The League of Nations was meant to be that peaceful roundtable to avoid future conflict.
However, it did not have the necessary power that it needed to remain since the United States did not enter into it, despite the fact that President Wilson established it, and all other members wanting the Untied States in it. It lasted from 1920 until 1946 when the United Nations succeeded it.