The funny thing is that all AI civs have been at war constantly from the beginning of the game (screenshot). I haven't seen this aggressive civs before, so I came up with the idea that maybe the AI civs feel they need to expand more. Since the land mass is so small, most civs end up with fewer cities than their optimum number, and start wars to try to get more land. On bigger land masses, most civs seem busy expanding into unclaimed land and after that gang up on some weak civ.
What do you think?