Nigeria restricts access to exchanges because crypto is being used to reveal true market prices for the naira, and undermine the government's fixed exchange rates.
This is how it will happen - you suddenly notice fiat economies have more and more dependencies on crypto (ultimately bitcoin of course, as govts can shut down the others).
https://www.ft.com/content/333309a5-196c-494a-8d68-506f6a19ba81