Sometimes an ally can be worthless; early in the game building up resources I never attacked an ally and lifted the siege on the Egyptians to keep them gratefully allied, only to have them attack me about 5 turns later. It would enhance the game if the diplomacy were improved and expanded, I like the militaristic aspects greatly but feel the campaign side could do with some positive diplomatic input, as at the moment, an ally can attack at any time and you have no benefits from alliances or any real penalties from attacking an ally.