Instructions
1. Go to the medieval 2 total war folder
2. go into mods- third age total war
3. go into data, world, maps, campaign, imperial_campaign
4. go into descr_strat
5. go to unplayable factions, the papal states is the dark lord and rebles are rebles.
6. make a backup copy just in case and cut and paste the two factions to playable list (i dont know if it has any effect, but i make them a straight line like the others).
7. go into third age, single player, campigan and you should get this picture-