Empirically disproven. You can invade a country, replace its government, create conditions that make reproduction impossible for the species of human living there then ensure that your vassal admits a different species of human that /does/ live in the stone age as replacementhttps://twitter.com/VesselOfSpirit/status/1201709225136648192 …
Sure, it's not quick process and it takes more than bombs but it does work.