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[Martok]

I disagree with Mailman. I think they wont be playable in the normal campaign, they will be an emerging faction, like the Romano-British.

That's what I'm thinking as well, but I dislike making assumptions.

It wouldn't make any sense to have the US as a playable faction in the main campaign. Both for gameplay reasons (i.e., they won't appear until later in the game); and also because, quite frankly, we just weren't that important back then. (To have us as a playable faction in the main campaign would be like having one of the numerous small German principalities as a playable faction.)