Good input from Jerec.
I was not saying necesarily to allow the building of AA defences in cities from the start, just that if you make this city improvement only buildable upon the discovery of a certain tech in the next version, you should bear in mind that this will make it even harder for the Republicans to survive the first few turns, and should therefore find a counter-balance.
There are a couple of other unknown factors that should be factored in to getting the right balance awell:
1) Partizans: You had intended to give these just to the Russians, but accidentaly you gave them to everyone except the Russians. Note that the only reason that Russia has got any partizans in this game is because at the end of each of my turns I am using the Cheat menu to take away the "No Russian" tech as we agreed upon in a PM.
This game flaw was only discovered after the SCW was over so it is unknown how the SCW might change if just the Russians / Republicans get partizans. My guess is that, unless you improve the stats of the partizans significantly, it will make little difference because:
a) The partizans are crappy at defence
and
b) The partizans cannot attack, and even if they could, their stats indicate that they would be crappy at attack.
Currently the partizans are only useful for occupying empty cities, stacking under other units to give the illusion of a powerful army, or as city fillers to exhaust the number of attacks that an enemy can throw against a city in 1 turn.
2) The Role of Germany in the game: As McMonkey mentioned, the Germans did not participate in this game and their assistance to the Nationalists might really throw things off balance. Having said that, the French did not participate either (after originally commiting to send assistance, Takimisikari subsequently ignored all my PMs and sent nothing).
I think you want to balance the SCW so that if all the Allies participate and all the Axis participate, it will be about even (sort of like a war within a war, or a prelude to WW2). In the real world the Nationalists won with the help of both Germany and Italy, but what would have happened if the Allies had assisted the Republicans??