Preventing another world war would have required significant changes to the political and economic landscape that existed in the aftermath of the first World War. Here are a few examples of things the Allies could have done differently:
Avoid imposing punitive measures on Germany: The harsh penalties imposed on Germany under the Treaty of Versailles, which included reparations payments, loss of territory, and disarmament, led to a deep sense of resentment and economic instability in Germany. This created an environment that was conducive to the rise of the Nazi Party and Hitler's eventual ascent to power.
Encourage greater international cooperation: The League of Nations, which was formed after World War I, failed to prevent the outbreak of another war. The Allies could have encouraged greater international cooperation and collaboration in the years leading up to World War II to address issues such as disarmament, economic stability, and global security.
Address the root causes of aggression: One of the underlying causes of World War II was the rise of aggressive and expansionist regimes in Germany, Italy, and Japan. The Allies could have taken steps to address the root causes of this aggression, such as economic instability, nationalism, and imperialism, through diplomatic and economic means.
Provide greater support to democracies: In the years leading up to World War II, several democracies, such as Spain, Czechoslovakia, and Poland, were threatened by fascist or communist regimes. The Allies could have provided greater support to these democracies, both diplomatically and militarily, to prevent them from falling under authoritarian control.
These are just a few examples of things the Allies could have done differently to prevent another world war. However, it's important to note that the geopolitical landscape of the time was incredibly complex, and it's difficult to predict how different actions would have played out.