5000 years behind, hadn’t even developed the wheel when the Euros and Scandinavians arrived.

If they want the land back? It can be done in theory. On the way out, reset all claimed lands back to the way it was circa 1600. Only fair, give them raw land so they can develop it how they want.

Also remove all mechanised industry, electricity, gas, oh and horses too. Gotta make it genuine. See ya! Good luck!