In OTL, the 20th century saw the speedy growth of the United States into a world superpower. Despite some failings such as Vietnam, the US has pretty much been able to maintain its hold on the top of the heap for a good amount of time.
WI the 20th century did not go as well for the USA as it did in OTL? What is needed for this to happen? How can we make this ATL 20th century the worst possible for the US, not including any wanks?