Challenge: Avoid the USA from reaching superpower (or even a power) status and keeping it as an emerging market in our days (something like Brazil or Russia in OTL)
PODs no later than 1900 and the USA should be kept with the same territory and natural resources as OTL.
Have the ACW go much worse, have it drag on to 1872 or so with the US government debt very high and having to pay high interest rates. Also due to this have a Communist uprising in 1880 or so . It remains a Communist dictatorship until the 1950s ruining its economy even further. Between all that the US might well be backwards enough.
But how a Communist uprising in 1880, when Communism was just starting to become a political force in some countries?
Could work bu IMHO Communist ideas would have to develop much more deeply inside the U.S society to the country reaching the point of a revolution....so I guess that 1880 is too soon for that...who knows something after 1917?