Then the person would make sure their armed guards are highly trained and have some fanatical attachment (through indoctrination) to the leader so they aren't just doing for their paycheck.
And where would this indoctrination come from? You going to be raising your own army from kids?
I guess it's possible, horrendously expensive, especially on your own dime, but possible. But what happens when you start storming houses, and losing troops? What happens when the other members of your society notice that you've gone and raised an army, and are now using it for conquest?
Well, look at history of the past 3000 years. This is exactly how it worked. You can "pay" for your conquest through the plunder you acquire.
You can indoctrinate people with religion, for example, or certain ideologies, like Communism or Fascism.
If you really have a strong army other people will have to submit to you. Also, if you are not entirely cruel and let people live under your "rule", then they might willingly submit to you or even help you. Also, you can always spread lies and rumors and make other groups seem to be worse enemies.
1: You won't be making any money while you're raising the kids. that's a 16-18 year investment in what, 3 to 400 kids? Whoo. You must be mighty rich.
2: Indoctrination doesn't happen overnight, Chief, you gotta get 'em young, before they start thinking for themselves.
3: Just exactly how strong an army can you afford? Remember, you've got to raise them on your own dime, since you can't have any plunder until you have an army.
4: How are you, by definition a monopoly, going to provide better services than the Market already does for these people? Do you honestly believe that propaganda is going to work in AnCapistan?