Alliance unique in-game tech/units/buildings

Here's an idea to make the players feel more involved with the alliance they choose.

Instead of just getting the passive bonuses, it could be made so that the player gets to create some unique units, buildings or even the chance to develop unique tech.

An example could be choosing Carthage and unlock the training of the priests of Baal in the temple/town center/etc. with different bonuses from (maybe stronger than?) conventional units.