Eh, it's still not quite true. Who are your European superpowers? Spain? We beat them in Cuba. Germany? Go ask Kaiser Wilhelm II. England? France? We had long since passed them as a "superpower." As to out tenure as a world leader, this country is 235 years old (since we declared ourselves thus and so). We've been a world leader for conservatively 75 years of that. That's about 1/3 of our time on the world stage. Not bad.
I think you are generally confusing WW1 and WW2. We did not just stumble by Europe because of WW2. Europe has been at war for the better part of 1200 years. You think the Middle East has conflict, check out or continental neighbors to the immediate east, they're a mess. To be fair, in the beginning, and throughout, it really was not a certainty that we would defeat the Germans, but remember, Hitler didn't want us in the War.
America was a World power prior to WW2, we became the World power after it.
