Also, have you ever considered the odd situation of Japan in the universe. Like, this break has actually given me the time to think about it and the more I do the more interesting my theories become. So I'd like to share them with you for comments and opinions.
First, what do we know about Japan in C&C?
Starting with Red Alert 2:
The game shows us two WW2 Pacific related memorials. Those being the Ivo Jima Memorial and the Arizona Memorial.
Even if we somehow excuse the later as saying that the Soviets attacked Perl Harbor (why would they?) the former makes no sense in a Soviet-American war setting. After all, WHY would the Soviet Union be putting such a strong fight up over Ivo Jima to warrant the historic memorial when the main war was happening in Europe?
And yet these two memorials are not only present in the game but carefully modeled and presented to us front and center in both sides campaigns. So clearly they are meant to be seen and noted as something important.
The opening cinematic of Red Alert 2 also shows us not one but two red phones on the table of the American president. One being labeled Moscow and the other Tokyo.
This means that in the 1970's Japan is still a major world player.
Finally given that Korea is independent in WW3 this means that the Japanese Empire as such has ceased to exist. Or is severely weakened. But the mere fact that it is Korea and not Japan that is the major allied colony / ally in the pacific while Japan is neutral also tells us that Japan was not conquered and subjugated like they were in our own timeline.
As for Red Alert 3 that game tells us that erasing Einstein from history in 1927 spawns an alternate timeline where not only is the Empire of Japan a superpower but they actually hold much of Asia including Hawaii. So much so that in the alternate 1970's they are one of the three leading superpowers rivaling the united states and Soviet Union.
So what is one to conclude from these?
If you ask me, my deduction is as follows:
In the timeline I am going for where Red Alert 1 and 2 are cannon but Red Alert 3 is not 1920's Japan is the same as in our own world. And it takes the same course as it does in our world through the 30's and 40's as well. During the 1940's and most likely immediately before or after but not during WW2 (otherwise we would be shown it in Red Alert 1) Japan picks a fight with the west and looses. But much like the Soviet Union they loose not thanks to an allied military victory but thanks to Einsteins technology. Thus by the 1970's they are diminished but not destroyed, much like the Soviet Union was.
They are thus enough of a world power to not be attacked by either side of the war and to warrant a red telephone (possibly meaning they have nukes) but not enough of one to join in. Or maybe they just figured they'd sit this one out for a change.