The challenge is, to create a scenario in which the U.S (or a state compromising all/part of what is now the U.S) suffers a defeat similar to the Iraqi defeat in 1991.
I.E Large technological disparity, complete loss of any kind of air control and the majority of theatre ground units captured/routed.
POD between 1900 and 1944
Bonus points if the war takes place in the late 1980s/early 1990s
Bonus points if the winning side is composed of a coalition.