More realms will equal more war. An alternative would be to allow dukes to fight their own wars (against other dukes), but for all the years I've tried I was told it was too much coding... and I believe that. I believe people leave BM because it grows boring. Distant wars and less wars combined is not what people look for in BM. Roleplay and storyline is a nice aspect, but I think most prefer the risk-like style of the game... conquering regions, spitting upon enemies and burning down warehouses. Since realms seem to have the tendency now to grow a little larger than they used to, it now takes longer to travel to the frontline. The problem here is that you cannot change player mentality. You would have to coerce rulers of large realms to let their realm sort-of explode to create many more realms and strife. They won't do that. Ultimately large realms can completely implode, because they have very little fun to offer to their players.
I know that an invasion is out of the question, but I just wanted to state that I have enjoyed every invasion on the New World/BT very much. It also seemed to draw more players to the island because invasion caused a struggle for survival, which was fun, because it meant the enemy was almost continuously knocking at your front door. Daily fights were no exception. Should it be reconsidered, I liked the idea suggested earlier of the multi's. While I wouldn't allow people found guilty of being a multi do it, I'm sure there's plenty of interested people who would not mind being part of an "invasionary" force. This would only allow a small change in the rules so that on every island there can be a multi-account, invasion-style faction. Which is crazy of course, because a multi is bad, mkay.