Russia needs to be producing the maximum number of units per turn that it can produce to hold off Germany, so it can’t really afford to buy another IC. Besides, there is no good place for them to put one anyway, as most of their territories would only be able to produce 1 unit per turn anyway, unless you try to build one on the German front where you wouldn’t get to use it anyway…
Germany doesn’t really need to buy another IC with being able to produce 16 units between Germany and Southern Europe in the first place, as they would need to be earning 48 IPCs a turn to even produce that many infantry, so an IC purchase for them is typically unnecessary unless you manage to take over Africa and are earning that much. I’ve never given it much thought as I’ve never had an issue with not having enough production capability with Germany’s 2 IC, but personally I would probably build one in Western Europe since it has the greatest production capability and already has an AA gun. Alternately, you may want to produce units one step closer to the Russian line, in which case the Balkans would probably be your next best position for three reasons:
1. Production value of 3 and 1 step closer to the Russian front.
2. Distance of Allied supply lines to take it: Russians typically are trading Karelia, Belorussia, and Ukraine at their best, and US/UK would have to bring their transports all the way to sea zone 16 to assault it.
3. Deadzoned by bordering both Germany and Southern Europe, so if the Allies do manage to take Balkans, it should be easy enough to retake it.
You probably also could build an IC in Egypt or South Africa if you want to better hold on to Africa, but as Africa is only good for the income and doesn’t directly help you win the game, that would probably be counterproductive.
An India IC is too easily conquered by Japan in 1942, though if you really want to build an IC with UK a South Africa IC can still be worthwhile to drop 2 inf per turn at least (2 tanks can be better), but again you don’t want to neglect your navy as the UK.
Transports are the way to go for Japan as they allow more flexibility and speed for the value (you can move 4 units from Japan faster for 14 IPCs with 2 transports than building an IC for 15 IPCs that can only produce 3 units). However, once Japan starts earning more money it becomes worthwhile to build an IC for the purpose of being able to produce more units, and as habs4life9 was saying, India is a great place for this (which makes UK building an IC in India even worse for the Allies as it saves Japan 15 IPCs for them to build it themselves).
The US has the most need for building an IC since its ICs start out an ocean away from any battle, but it also has the least possibilities, so most of the time the US doesn’t build any new ICs since it doesn’t have anywhere to build them. Since China is US controlled in this version, the US can consider an IC in Sinkiang only if they know they’ll get lots of support from Russia to keep the Japanese from taking it right away, however, this isn’t usually much of a help since it can only produce 2 units per turn. The China territory itself is too vulnerable to the Japanese. Brazil can produce 3 units, but is only 1 step closer than EUS is anyway, so that isn’t too much help. The best option for an IC for the US would be for them to take Norway and build an IC there, bringing over the AA gun from EUS on a transport from ECanada to protect it from German bombers. This lets the US build 3 units directly into Europe where they can immediately be of use against Germany. The only problem is that typically the UK takes Norway since they are closer and it provides them with some much needed income with Germany taking over Africa, but it may still be worth it for the US to immediately have units in Europe.
