Yeah, the AI would be tremendously hard. I guess, after a second's thought, that you could create 'groups' of many regiments. These would act "with one mind", as it were, which would take less processor time... with occasional random fluctuations (like a person running away because he's a big sissy). You could simplify the AI for regiments that aren't visible (or possibly run an algo to find the 'most interesting' units, such as those with lead characters, and concentrate on their AI). I'm not an AI guru. If anyone is, feel free to start a topic on this

I'm tripping over all these links: here's one to Craig Reynolds, the originator of 'boids' (flocking stuff). His site (check out the steering behaviour examples. They're very nifty.)