In the Total War Launcher, open the Mod Manager and check the box to allow "out of date" mods.
Generally, place the Scripts and Base Pack at the top of your list, followed by the Models Packs in numerical order.
To play the full campaign, you must subscribe to a specific set of packs. The most reliable way to access these is via the . Link / Source Base Pack (Campaign Alpha) Steam Workshop - Base Pack Required Models (Packs 1-9) Listed under "Required Items" on the Base Pack page Scripts Pack Essential for campaign mechanics (found in Workshop) Optional Music Mod Steam Workshop - Music Mod How to Install & Load Order
MK1212 isn't just a unit reskin; it’s a total overhaul of Attila's systems: Medieval Kingdoms 1212 AD Base Pack - Campaign Alpha