As many of you know, when you unpack the game files, there are two files named descr_georgraphy_new.db and descr_georgraphy_new.txt that must be deleted in order for the game to function. Well, I had unpacked the game long ago and, having just gotten back into the game, I reinstalled Medieval II. The game CTD'ed every single battle I entered. I finally discovered that the old unpacked files that were lying around in the Windows Virtual Store, were affecting the gameplay. I deleted those two files and the game worked fine. If you're not a modder, but for whatever reason unpacked the game, than these files in the Virtual Store can be located at C:/users/[USERNAME]/AppData/Local/VirtualStore/Program Files (x86)/SEGA/Medieval II/data

Hope this helped!