i'm not 100% sure about this. but, it seems, rebels pop up more frequently on VH campaign difficulty. starting money seems to be the same. i've heard: on the VH campaign map difficulty, the game engine uses VH tactical map bonuses when autoresolving against a human player. the same, supposedly, applies also to naval battles. it seems right, since my ships would lose even when considerably outnumbering the AI's fleets. i have not noticed any other differences though.