Kind of depends what kind of governmental system you have and how you want to present it. Also, how many members and who has the power in that alliance.
A "syndicate" for example, is usually associated with organised crime. An "order" is usually a group founded a shared philosophy rather than a conglomeration of territories. "coalitions" tend to be a temporary arrangement of convenience rather than something that is a unified organisation - it implies two or more organisations working together for a limited duration.