Ensure you have Medieval II: Total War and its Kingdoms expansion installed.
Right-click the game in Steam, select Properties , and in Launch Options , enter --features.mod=mods/Third_Age_3 . Optimization and Troubleshooting medieval-2-total-war-kingdoms-1.5-third-age-3.2...
It is highly recommended to apply a 4GB patch (or "Large Address Aware" tool) to the medieval2.exe and kingdoms.exe files to prevent crashes during large battles. Ensure you have Medieval II: Total War and
Players lead factions from The Lord of the Rings , such as Gondor, Rohan, the Elves, Dwarves, or Mordor, in a struggle for control over Middle-earth. and in Launch Options