Why were world leaders optimistics in 1920 that future wars could be avoided?

World leaders in 1920 were optimistic about avoiding future wars largely due to the establishment of the League of Nations, which aimed to promote international cooperation and resolve conflicts through diplomacy rather than military action. The devastation of World War I fostered a strong desire for peace, leading many to believe that collective security and disarmament could prevent future conflicts. Additionally, the widespread belief in progress and the potential for social and political reforms contributed to this hope for a more peaceful world order.