In MoM, you could either recruit the nationals in the town you conquered, or convert the town to your own population. So, you could get powerful units from other races, but since other races have another alignment than your nation, you had had other trouble aswell (income/unrest/etc.) unless you converted the population. I really really loved that game, I guess I'm not the only one who only got to play Dominions just because he wanted to find a substitute for MoM, right?
