Additional installation instructions only for Steam users:
1. Install all parts of the mod as instructed above.
2. Open "Steam/Steamapps/Common/Medieval II Total War/mods". There you will find all your installed Kingdoms campaigns as well as the "Third_Age_3" modfolder.
3. Edit the name of one of the Kingdoms folders (americas, britannia, crusades, teutonic), preferably your least favorite campaign. The new name doesn't have to be anything specific.
4. Change the name of the "Third_Age_3" folder to the former name of the Kingdoms folder you just edited. For example, if you edited the "americas" folder, the "Third_Age_3" folder should be named "americas".
5. Select the appropriate campaign from the steam menu. If you renamed the "Third_Age_3" folder to "americas", select the americas campaign. If you named it "crusades", select the crusades campaign and so on.
6. Steam will now launch the mod.