So an example of what you're saying is 3 players command 3 armies (Let's say Vaegir, Khergit, and Rhodok)
The Vaegir could have his troops hold position hoping to fight defensively so that the other 2 would fight each other. The Khergit would use commands to tell his troops to attack only the Vaegirs because he reasons that if he tries to take on the Rhodoks he won't have much luck. The cunning Rhodok pauses only a moment so that the Khergirs and Vaegirs are focussing on each others' throats rather than his, and then commits his troops to seek out the distracted Vaegirs. What ensues is a cataclysmic battle that will leave the land horribly scarred for ages to come...
Nope. Can't think of a thing. I only play single player.