Well if you look at the first KB...that's exactly how it was. In my eyes, that's the beauty of the game...I am not locked into using only specific units.
Although if my memory serves me correctly, that doesn't mean you can just mix and match *any* units. I think if you had evil units (undead) mixed with good units they would get pissy and disband. At least that's the way I remember it...been 18 years since I played
