Well, as Paul Atreides himself explains in the sequel to Dune, his Fremen Jihad causes the death of over 60 billion people throughout the empire. You can safely guess that the vast majority of them are innocent ordinary people, but just not important enough to pause over on the path to grand prophetic dreams. Basically, from when he takes power again, he becomes a genocidal monster in charge of an army of murderous fanatics, and then he spreads this right across the empire, well beyond Arrakis itself where he already caused all kinds of chaos.
The story is a classic narrative of hoped-for ends being used to justify horrible actual means, but cloaked in space opera.
No, it's in the second book actually, (spoiler alert) which covers the time in which Paul's rule has been firmly developed following his enormously bloody jihad across the Empire, and the time after his death, after which his son Leto succeeds hims and lets himself be symbiotically covered in baby sandworms to turn into the eventual god emperor of the Imperium, ruling for 3000 years. (If I remember correctly)
The story is a classic narrative of hoped-for ends being used to justify horrible actual means, but cloaked in space opera.