Quoting davrovana, reply 28
It is a war game.
I am pretty sure alliance,trade and economic treaties are actually in the game to be used.
Yes, they are meant to be used...in the context of war.
Consider the subtitle of the first game: War Of Magic. I am simply suggesting that it is a game focused on directly dominating your opponents - it contains all the 4X elements, but cultural and diplomatic domination is subdued, while unit customization and tactical battles make it clear war is a emphasis of the game concept.
Diplomacy could be deeper - but it's not necessarily the best move for this 4X game. I think the designers intended direct conflict to be the game's focus, through armies, heroes, or magic.