Imagine you’re a conqueror. You’ve just vanquished a horde of barbarians in some faraway land. You want to claim this land as part of your empire and make the barbarians into your laboring subjects. But they have nothing in common with you. They speak a different language, practice a different religion, have entirely alien customs from the civilization that spawned you. What’s more, they’re a freedom-loving people, and they despise you for ruling over them.

You have a massive army currently occupying the land you’ve conquered and with it, you can force your will on the subjugated population. Your soldiers flog anyone who gets out of line and summarily execute anyone accused of a serious crime or act of rebellion. The barbarians are terrorized into submission. But the more you oppress them, the more their hatred of you festers. Small, clandestine acts of rebellion are becoming more frequent rather than less. You’re constantly monitoring your subjects to find out if they’re plotting against you. At any moment, you fear, a serious revolt could erupt.

It’s extremely expensive fielding this large army with its far-flung supply lines, and keeping them stationed here means they’re not out conquering new territory for you. Sometimes you think you’re losing more than you’re gaining from your effort to hold onto this slice of turf. If you’re going to keep it for the long term, you need to find a more efficient way to control the indigenous population. Killing them all is out of the question, because you need them to till your fields and build the city you’ve erected in your name. What you need is for them to choose to obey you. You need them to have a reason to do your bidding without your having to raise the whip.

You try out a few innovations. First of all, you start converting them to your religion. They’re actually quite well-disposed to this, because they see from their own humiliation how much mightier your god is than the ones they’ve traditionally worshipped. They understand that they need to win his favor. So they accept your god as the greatest in their pantheon of deities.

But you also impress upon them that your god is a different kind of god than theirs. He does not demand blood sacrifices or rituals to appease him. Instead, he demands something else: he insists that his followers live their lives according to his moral code. Those who behave in accordance with his rules will be rewarded after their death. Those who fail to will be punished mercilessly in the afterlife.

The barbarians resign themselves to their new circumstances and begin to live according to the rules of their new god. They begin to see that their subjection to your rule is not just a temporary misfortune imposed upon them by the force of your army. It is, in fact, divinely ordained. Even more than that: their obedience to you and your deity is what separates them from other, lesser men who have not yet discovered His awesome power. Those who obey you, his agent on earth, partake in His godliness. Those who do not are little better than beasts.

Now your army can withdraw from the territory. Your subjects will not just accept your rule; they will fight for the opportunity to serve you as warriors, spreading your righteous reign to the uncivilized heathens of the wildernesses beyond. Your rule is sanctioned by the heavens. It is good, and those who submit to it are good, too. Those who refuse to are evil.

Your power has now become legitimate, which is to say, it’s perceived as legitimate by those who submit to it. As long as you sustain that legitimacy, you won’t need to fear rebellion. For that reason, however, rivals will no longer rely on their armies alone to contest your rule. Their principle weapon will be to undermine your legitimacy. Wars of arms fought by soldiers will be preceded by wars of words fought by priests, philosophers, and demagogues. Where once your right to rule was merely a function of the violence you could marshal to back it up, now it is a thing of ideas, beliefs, and arguments. You need not just soldiers, but intellectuals to uphold it.