Why do you think americans supported participation in the un after wwii when they had opposed participation in the league of nations after wwi?

After WW1, most Americans were in denial of their place in the world. They went on a period of "isolation" from Europe. After WW2, they realized what President Wilson said was correct: that another World War would happen, even worst than the first, if we do not take action against it. America would have to participate in settling world problems if another Great War was to be prevented. 

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