Alexander the Great made his conquests by building a really good reputation for war, then leveraging it to get tribute agreements while leaving the local governments intact. This is a good way to do it when communication lines are slow and unreliable, because the emperor just needs to check tribute once a year to enforce the agreements, but it's weak control.

If Alexander could have left perfectly aligned copies of himself in every city he passed, he could have gotten much more control and authority, and still avoided a fight by agreeing to maintain the local power structure with himself as the new head of state.