That reminds me of how i used to handle GA campaigns in MTW: I usually attacked only my nearest neighbors at the beginning of the game, and then i would just develop those provinces to their maximum. The interesting side effect is that one of the AI factions always emerges as THE superpower, so, if you let it grow (and sometimes, just for the challenge, you WANT to let it grow), you can have an ultimate showdown by the late game.

In RTW, this showdown is almost always against rome (either by civil war or by fighting it united). With one notable exception: Carthage. In my carthaginian campaigns, i always manage to destroy rome early (perhaps i let the senate live, just so i can get the improved bodyguards). So, its harder to predict who will you be facing in the end. In my cases, it has been seleucia(yes, they beat the egyptians, with a little financing...) adn Macedon(these guys did it on their own). It gets funnier this way...