Good question. What I need to do is to make incentives to not bulldoze these nations. One idea is for the Tetrarchy of Judea to provide regular tribute which makes you want to stay allied to it. For the African nations i debated making the legions much less effective in desert terrain, but historically they could fight nearly anywhere, so I think the makeup the the troops will help with that. If anyone has any ideas as to how i can make the Romans harder to play as, just give me a shout and il take them into account. :)