World War I was indeed a prelude to World War II. WWII can also be viewed as a continuation of the same struggle. In both wars, the Germans and Austrians fought against the French, British, Russians, and Americans. In a sense, there was just a twenty-year truce between the two conflicts. The League of Nations failed to prevent World War II, but we cannot be certain that American membership in the League would have been enough to prevent WWII.
Fortunately, there has not been a World War III. Has the United Nations prevented that catastrophe? Has American participation in the UN played a decisive role? There are no determinate answers to these thought-provoking questions.
One could argue that the North Atlantic Treaty Organization (NATO) has been the key to the absence of a third world war. The Soviet Union understood that any attack on a Western European country would face a formidable coalition. Perhaps an earlier version of NATO would have deterred Adolph Hitler, but we cannot be certain.
Hitler's appeal to Germans stemmed, at least in part, from his promise to overturn the Versailles Treaty. Germans thought they had been unfairly blamed and punished for WWI, so they welcomed Hitler's promise to set it aside.
In addition, Germany was not the only source of instability during the interwar period. Japan was aggressive and expansionist. Italy and the Soviet Union were dictatorships under Benito Mussolini and Joseph Stalin, respectively.