This thread might be dead already (It's pretty worn out) but I want to try to add something to both sides of this argument. Dual-wielding is most certainly possible, and has indeed been done before. The argument that a person's offhand is not strong enough to hold a weapon is kindof silly, because the difference between the two hands in almost never that much. For me at least my left hand is stronger, while my right hand is more dexterous.
The biggest question in my mind when I think about whether dual-wielding (Which sounds so DnD that I won't say it ever again) is whether or not it would fit with the history that the game does draw from. I know that none of the factions are ar were likely ever real countries, but the were obviously designed after real countries in the middle ages.
The Swadians have always made me think of the Franks and France. At the very least they are representative of Western Europe circa 1300. This is at least how I see them when I'm playing this game. They have heavily armoured cavalry, and their ranged units are obviously drawn from society's lower tiers, and are stuck ground-pounding. The crossbow was more popular than some people think in the middle ages, even with the church trying to ban in. So if the Swadians represent Western Europe circa 1300, would any Swadians use any kind of two handed fighting style? Probably not, because as several people have pointed out, one handed weapons were generally insufficient against thick plate armour. Unless you struck at joints or holes, which must have been faiurly small even though I've never actually seen a real set of armour, you just wouldn't be killing the person inside. Having two weapons which can't pierce armour wouldn't help, so the probably would have stuck with the one, larger weapon. I cannot think of any examples of Western European two weapon fighting, at least not on a scale large enough to have been a significant, encompassing cultural aspect. So for two-weapon fighting, Swadia is pretty much out of the question.
The Vaegirs are a bit harder for me to place historically, but the combination of horse archers, mail armoured knights and rather wild looking peasantry makes me think of Eastern Europe, specifically Russia and MAYBE some parts of the Byzantine Empire (Although I'm not sure at all about the later). I can't see Vaegir knights using two one-handed weapons, because the great axes they use just fit them too well. I really don't have any specific reason why they fit so well, but they just do. The cavalry archers would probably have trained much more in horseback archery than in any kindof melee fighting, so they probably would have stuck with single weapons, which would seem easier to learn to use. Footmen and Veterans are hard for me to place culturally, because I have a lot of trouble finding a single overall influence for a Vaegirs as a whole. The Footmen and Veterans, as well as the Archers seem to be throwbacks to Europe in the Dark Ages. The Dark Ages were predominantly filled with Barbarian warlords and warriors. I can see no reason why none of these wouldn't have fought with two weapons at once. There isn't much documentation about the Dark Ages though, so it's hard to be sure. Guards and Infantry are no longer, Dark Age units, but remind me of Middle Eastern warriors. These were much more disciplined and more inclined to fight as armies, rather than collections of single warriors, than western Knights and troops, which to me suggests a sword and shield combo would have been favored. Two weapon fighting seems (historically) to be a fighting style for single warriors, not armies.
To back up that last point, I'll use Skree's example of Miyamoto Musashi. He, from all accounts, was a famed duelist. Duelists are single warriors, and are not nessesarily the best soldiers. In this game you recruit soldiers, not duelists. Most of the people, likely all the people, you recruit would have been trained to fight with one weapon, or one weapon and a shield because they are trained to be soldiers and not just warriors. Because they're both soldier populations (and farmers and peasant women) niether the Swadians nor the Vaegirs are likely to have anyone swinging two weapons about.
That isn't to say it shouldn't be found at all in the game, the Sea Raiders are obviously Vikings (I usually just call them Vikings) who were more a group of single warriors than any other group, ever, at least in my mind. They're often depicted as wielding two axes and going berserk in battle. I'm almost positive that's a bit of a gloss, but it is at the very least how their contemporaries would have seen them. The game wouldn't lose anythign for me if a few Sea Raiders would run around swinging two axes at once.
The number and size of factions which would use two weapons simultaniously and the number and size of those that don't are so disproportionate that it would feel out of place for the Player to be able to wield two weapons. Swadians, Vaegirs, Kerghits, Steepe Bandits and almost all the nuetral units would almost certainly not use two weapons at once. Sea Raiders and possibly some other bandits might dual-wield (Damnit! I fell into the DnD trap and said it) but certainly not exclusively. Because of this I think that as it is now the game should not include dual-wielding at all.
If dual-wielding (I've given up on not saying it) simply has to be incorporated into the game, it should be a skill that is hard to aquire, not even appearing on the character sheet until a certain requirement is met or a quest is complete. Or perhaps have the player choose a nationality when creating a character, and only nationalities which would include dual-wielding culturally and logically would allow the skill at all. Other nationailities could perhaps have some other kidn of bonuses to maintain a balance in the gameplay.
That's all I ahve to say, I'm sorry for being so long-winded, and if you read the whole post I appreciate it.