Medieval II: Total War has a surprisingly active and vibrant mod scene for a game its age. Highly regarded among old-school Total War fans, the engine it's built on has enabled many wonderful creations from simple vanilla overhauls, to complete setting changes, and more. Being a game set during medieval Europe, you can imagine the kinds of mods available now. From Westeros to Warhammer, Lord of the Rings to Three Kingdoms China, there's something for everyone, and we've curated a list of some of the more popular picks below.
Do note that any mod that uses a third-party IP probably isn't endorsed by that IP's owner, and even Creative Assembly frowns upon these kinds of mods for the newer Total War games where the studio has more control. As such, we won't be providing download links for them, but if you go to sources like ModDB it won't be hard to find them if you are interested in checking them out.
Also note that all mods below, unless stated otherwise, require the Kingdoms expansion, and you're probably best updating to the 1.5 patch as well.
RELATED LINKS:
Medieval 2: Total War cheats and console commands
A Witcher mod is in the works for Medieval 2: Total War
The Witcher becomes a strategy game in this Total War mod