Ok so I unlocked all factions but how...

[MiniKiller]

I would like to play as the Aztecs but I get booted to desktop when I try...havent tried the Mongols or the Timurids yet but is there a solution to this? I found a mod that allows play for this factions but adds to much otehr stuff for me...I just got it and want to play without mods (past getting these fations to work) for my first campaign or so

thanks