Alpha Centauri also has excellent diplomacy (and that game is 8 years old!!). In my Bactria game I had Ptolomy, who had been my ally for many years and who I had repeatedly saved from extinction at the hands of the Seleucids turn round and attack me as soon as I bordered them. Grrrr. The last night, for no reason whatsoever, Macedon (who are the other side of Asia Minor from me) decided to blockade my port at Antioch, thus putting me into another war.

Sadly I don't think this suicidal diplomacy AI has been fixed in MTW2 going by the German review thread and CAs statements to the effect of "increased challenge by the AI attacking you".

Grrr....