Furious:
From my observations of the MA, most people don't care if their country wins of loses. So I really doubt that a significant number of players will come to the aid of their ally. In the current MA setup when Knights are pounding Rooks and about to reset, then it is in Bish's "best interest" to come to the Rook's aid and prevent the reset, and not "lose". But if this ever happens I have never seen it. I don't expect it will happen in your scheme either.
4 sides you often get big A picking on little B while big C picks on little D.
You think C will attack A. But it is just as likely that C and A are allied as that C and B are allied.
You will always have the problem of the 2 big countries being allied. There is no guarantee that the 2 sides of the alliance will be balanced any more that there is a guarantee in the current MA that all 3 countries will have roughly equal numbers. Think how much worse the gang-banging will be when one team outnumbers the other team. However in the 3 country system, the 2 big guys do end up running into each other at some point because there is nowhere else to go.
If most players cared about winning or losing the war the current 3 sided system would work very well at solving the problems you want to solve. If people cared and knights had 30 bases, Bish 20 and Rook 15, then Bish and Rook would immediately turn on Knights until the balance was restored. But they don't. And in your scheme they won't either. Did you ever see the effects of the 4 country system in Warbirds? It sure doesn't seem like it. I played it with 4 MA type countries and with 2 pairs of allied countries and the gang-banging in both setups made the AH MA look like perfection in terms of balance.
Most player's have their own agenda. They might only have 30 minutes to play and they just want to shoot something down before they log. If observing the MA teaches us anything, it teaches us that most players don't give a crap about "the war" and don't care if their country wins or loses. I don't care about this and I don't think anybody in my squad cares about it either. And you can't make player's care. We all do this for fun. HTC might be able to make the strat more fun and that will cause more interest in the "war" but I've never seen any system capture the interest of any but a small minority of players. And you can't penalize players for not caring. The play it for fun, and if you try to coerce them into some style then it is no longer fun and they just log off (or switch from WB to AH).
Hooligan