Whoa, whoa, watch the strawman arguments. A proper argument is claiming that Russia should have allied themselves with germany after being invaded. No, they didn't, they went to war and together with the united western front CRUSHED the Nazis. So history has an example, and it's actually a counterexample to your claim.
The anology was with the western allies deciding to ally with a Russia that right up to that point they believed would invade them given half a chance - or, perhaps, a Russia that joined with them out of necessity despite having been invaded by said allies a couple decades previously. It's a pairing that almost broke out into war the second the threat it was meant to defend from ended, but it still existed for a time. If this game manages to get that sort of distrustful agreement across correctly I'd love it - of course, that's certainly an important "if".
For that matter, I don't think there's a canonical war between any of those during the Second Era up to the point this game is set, and in fact the most recent one I can think of is the Nords showing up at Red Mountain, over 2000 years before the Second Era began... not that I don't doubt some combination of two of those three managed to end up in a fight at some point after that.
The thing is, they should be at war right now, not united. And it shouldn't be a racial alliance either, but a regional one. What if I'm a Breton who lives in Black Marsh? Well, there are bretons who live in black marsh, but the game doesn't much care for them with this setup...
Well, the strict association of races with provinces has been a bit of a problem in the series from the beginning (the first two games actually just showed you a map of the provinces and had your race based on which one you picked). So, while it is a problem, it's not a new one.