Empires! How do your empires rule?

Empires rule in many ways in real life and in few in fiction! Empires need control over their citizens in some way, so, how do the do it? Do they rule through the classic FEAR? Do they control vital resources? Do they assimilate others into their culture by making it favorable to follow the customs of their rulers? Do they provide security from outside threats in exchange for the privilege to rule the land? What is it?

Knowing how your empire rules can help you better flesh it out and make it more interesting! Or you can use, because PLOT! One works the other doesn’t.