I strongly believe, and this fits perfectly with the "smaller realm" idea, that splititng up your own land will more easily lead to tension. You know, because Duke A thinks that adding a region from Duke B would just be marvellous! The problem is that I still want these duchies to be united under "the same flag", i.e. they form a realm although they are technically, according to the game mechanics, all different realms. You could do so through a federation but that beats the point of having Duchy A fight Duchy B (as it would get all duchies involved, something you do not want). Next to that it would demand some form of OOC-commitment to at least somewhat act as "one united realm" and for all I know humans are prone to lying and OOC-commitments kinda fall under the "clanning" thing.
But if you do that, then the point of each small realm is to re-create the original, big realm. You will not get people to break up just to recreate what they already had but be all friendly in the face of outside enemies: that is just not SMA (and even outside Dwilight is just meta-gaming).
