I just finished an Emperor level game as Morocco and beat Sejong in a Space Victory by turn 350s with 0 battles or wars against any major Civs because of my extremely high diplo status.I remember the original design goal with Civ5 was to make a competitive AI that realized it was playing a game and tried to win. But there was an ENORMOUS furore on here about lack of diplomacy?
I had DoFs with India / Songhai / Sweden / USA / Korea / Brazil throughout the entire game and everyone hated the Huns.
Askia wanted to backstab me numerous times but I'm guessing he didn't want to face the diplomatic consequences. I had trade links with basically everyone and the USA / Brazil were following my religion. I didn't even build up a large army because I was too concerned with building enough Tourism to fend off Brazil's influence.
I won by 1 spaceship part in the end because pretty much everyone friended another and traded RAs. So there was some diplomacy going on in my game but the AI didn't play to win. I thought ideological differences would create some hostility, but it never materialized
In a sense there is diplomacy, but it was a very passive, boring game and I'm looking forward to the fall patch.