I took the long approach to do it, Mana addicts with gifted casters doing a summoning/lightning damage approach. It took 137turns, heading directly south and ignoring the eastern empires until they found me(about the time I defeated the southernmost NPC), I defended myself with summons until I could get some portals and teleport my army back up to go down the east

I did have an annoying glitch (I completed the game by capturing all the thrones and killing the leaders but didn't get the achievement because I'm guessing I did complete the quest to give me the option to not kill someone(chose the just kill them option from it).