Since the Axis each have a starting income that is divisible by 3, originally I had the mechanics for merging theatres as a function of the Axis country either increasing their income by 2/3rds more than their starting income, or decreasing it by 1/3rd less than their starting income. (Which sort of dovetails into the “2 out of 3” rule for Victory Cities.)
This effectively worked out to:
Changing it to a uniform +10/-5 made the math a little bit more intuitive, but it also means the USSR doesn’t have to get beat up so much (down half their income, possibly even losing their capitol) before the US/UK are able to jump in and help.
In terms of territorial gains/losses, this typically works out like…
+10 Germany = Karelia, Ukraine, Caucasus, Persia
-5 Germany = Finland/Norway, Eastern Europe
+10 Italy = all of Africa, plus Brazil or Eastern Canada
-5 Italy = all of Africa (except for one territory), or losing Southern Europe
+10 Japan = all Chinese territories, plus India or Philippines
-5 Japan = Indochina/Burma, Manchuria
So, Italy probably has the toughest time (as one might expect) but none of these scenarios are completely out of the realm of possibility.
@Midnight_Reaper There was a group of pieces made by pewtercraft each had their rules with them for use with axis and allies from that time period of MB. not sure if the rules can be found anymore and pewtercraft has been done for a while. The ones I currently have.
Anti tank guns
Mechanized infintry (this is in game now)
Troop Trains (versions of this are now in game)
Scorched earth ruins
Some of the ideas are good if they are tweaked a bit.