User blog comment:Fegaxeyl/No US superpower - but how?/@comment-32656-20110801015616

No WWII would not mean bankruptcy, etc in the USA - they would eventually get out of it, as they started to do before the buildup for war even started. All it did was make it faster.

Only really one thing I can think of. During WWII, the US government actively planned how to deal with the influx of soldiers coming back from war. They did not do it after WWI, and there was a recession almost immediately. Given the state of things at that time period, and politics, just have them do nothing. While a collapse is pretty well impossible, a much weaker USA, along with no massive Marshall Plan like in otl, may well be doable. It'd be a minor recession, rather than a boom, like after WWI, but would weaken them - call it a setback of maybe 5-10 years. Should have the net effect you desire.