I couldn't find much on it, but i did find someone else explaining it on this forum:
http://medieval2.heavengames.com/cgi...7,8447,330,all This is what the dude said
This is what the dude said,
"you can just wipe out a faction, BUT you have to be doing it on the Long Campaign. Once you wipe them out, you don't even have to finish it, you can just exit and go back into the Grand Campaign menu and you will have it unlocked. (that's how it worked for me)". <--- That's also how I remember it i'm pretty sure. But I just thought if your guys implemented something like that i'd be pretty cool. Maybe for some less important factions that you where or weren't planning on having playable. But its just an idea, figured I ask about haha.