Final answer:
Woodrow Wilson's idea for preventing future wars was the establishment of the League of Nations, although it was ultimately ineffective leading to the formation of the United Nations.
Step-by-step explanation:
Wilson's biggest idea was to have a League of Nations which required all countries to work together to prevent war from happening again. The League of Nations was a pivotal component of Wilson's Fourteen Points, specifically the fourteenth point, which aimed to establish an international organization dedicated to mediating disputes and upholding global security. Unfortunately, despite its idealistic goals, the League of Nations struggled to halt aggression and was ultimately deemed ineffective in preventing the conflicts that led up to the Second World War. Post-World War II, the concept evolved into a more robust international body, the United Nations, which sought to learn from the shortcomings of the League and provide a stronger framework for collective security and peacekeeping.