Tsathoggua

Is there any way to get the AI to respect my borders? Even when I'm overwhelmingly superior to an AI player, they freely admit they don't respect my territory and ask for an open borders treaty. It seems as though no AI player actually stays outside of my territory and I don't have the option to yell at them to get out in diplomacy...

Is there any incentive to diversify your fleet with ships of different sizes or is it best to just crank out the biggest ships you can make (as in Galciv 2)? I'd personally prefer some incentive to have a mixed fleet (i.e carriers, battleships, cruisers, frigates) rather than just a fleet packed full of battleships.