i heard of something called feasage recently, it was something about factions basically defending yours since you cannot hire lords. What is feasage and how do i get it? Can you in any way have vassals? if so how?
some people have suggested backing a claimant to a throne, and once you have the backing of a few lords rebeling against them. (i am unsure if you keep them on your side)
Or maybe they reffer to the nation relations, im not sure however if nations with good relations will ride to your rescue on their own. I do know that if you start a fight with an enemy near a friendly army they can join you in battle (i love leading a larger army towards a 3rd party then turning it around to out number them)