You'll need to jump through the same hoops as I mentioned above for landed merc bands.
If you usurp their title via claim all their vassals become yours, including the massively powerful Mamluks (Fatimids), Ghilman (Seljuks), and/or Varangian Guards (ERE.)Īlso be in the lookout for any merc bands that have conquered land off their former employer. This is the #1 reason why I would go to such lengths to conquer the Seljuks, Fatimids, and especially the ERE via claimant war. If they have no land you can outright forget about ever revassalizing them again. In the very unlikely chance they are landed, you'd need to have same religion/culture (force vassalize with Jade Dragon DLC) or have a claim on that title specifically (marriage claim only.) They're are damn hard to revassalize. When someone eliminates their liege, they become independent. The guard (as with all mercenary bands) are tied to their liege.