Here's an idea:
Don't do away with main, but make it the conquerable island. The kingdom who 'owns' it gets to make the laws of the land, decide who can and can't go where, decide prices by putting taxes on all the items bought in the store, and all the extra platinum goes to paying better guards, which helps prevent other kingdoms from taking over or not following the rules. You could put guards in front of the dungeons, and let only those you want in, but you couldn't deny those without a kingdom, since that would be bad, and they're kind of citizens of main. But it would work, and would definately encourage many, many kingdom wars.
