The general feeling in the county 1939 was that we had been tricked into involvement in WWI at the behest of the British, who's real interest was to preserve the economic benefits of their empire by excluding others, including Germany and the U.S., from foreign markets which they controlled. It was felt, generally, that WWI for all its high ideals, had really accomplished nothing and that the U.S. would have been far better off by not getting involved and letting the European powers fight it out to a final resolution. To his credit, Roosevelt understood this, and the Lend-lease Deal worked out to save Brittan from immanent collapse required that it effectively dissolve the Empire within several years of the war's end. So it did, and the U.S. has been profiting from that deal and follow-on Breton Woods Agreement to the present day.
The world would have been better off if the Central Powers won WWI.
They would have taken care of Russia, so no Bolsheviks. The old imperial order would have remained in place in Germany, so no Hitler. Britain would still have her Empire.