The only exceptions are the faction leaders themselves. Once you’ve become a vassal (or a ruler) in Mount & Blade II: Bannerlord, you’ll be able to convince lords to join your cause. Mount & Blade II: Bannerlord – Recruiting enemy lords For more information, check out our Mount & Blade II: Bannerlord guides and features hub.
Note: This guide is intended for Mount & Blade II: Bannerlord’s early access stage. However, there’s a way to have enemy lords betray their own kingdom. Truth be told, most of these actions - especially those that increase your renown and influence - will lead you to unending war. In our series of guides for Mount & Blade II: Bannerlord, we’ve already detailed how to become a mercenary or a vassal, build up your clan’s rank, and play politics with the other lords in your kingdom.