Maybe if this does well an alternative scenario with a global map and the USSR as a 4th power:
Set in the same period, but the 4 power blocks have fought each other to a standstill. Germany would have expanded to swallow eastern Europe and north Africa, and much of the middle east. Japan will have completed the occupation of China, and maybe driven through India to meet Germany in Persia. USA & what remains of the UK’s empire is merged into a single power controlled from Washington. The Soviet government has moved from threatened Moscow to the relative safety of the Urals.
The idea would be that as a result of primitive nuclear weapons and economies devastated by war, power are no longer able to manufacture and maintain advanced weapons. What you start with in terms of bombers, jest, battleships and so on is what you get - nobody has the capacity to build any more. After a few turns you will no longer be able to maintain complicated machinery, and the units will become redundant. That’s when the new cavalry and archer units come into their own…