The age of Enlightenment was the final (nuclear)war between the Surakian (who was still alive at the time)Vulcans and the Romulans which happened in the 4th century BC (earth time), which is when Rome was really starting to get on it's feet and Socrates was executed for diddling his (adult?) students. We saw Archer have a dream about this, (katra sponsored VISION.) where he met Surak, and this also dates to that telepathic WMD Picard was looking for in TNG Gambit that was rendered useless if you didn't have violent thoughts for it to use against you as a catalyst inside your soul.
At the end of this war.
After winning or losing.
The Romulans left Vulcan.
In space ships.
Coexistence is for chumps.
(in TOS some god says in Return Tomorrow that Vulcans had been in space for half a million years.)
You could say that the Romulans lost and ran away as refugees, but how could millions of Romulan astronauts trek out into unknown space to form hundreds of colonies after their homeworlds biosphere had been wrecked by thousands of nuclear explosions in population centres? But frankly if they could have just left easily
... Why start/fight a nuclear war? Did the Saurakian Vulcans start the war? but if the Saurakian Vulcans had won the war, what were they going to do with the millions if not billions of surviving Romulans?
Eviction or execution?
The only way that the Romulans would have been able to leave, using half the planets natural resources to build massive space arks, is if they won the war and still controlled those resources, but Vulcan was a much shittier planet after the war not worth keeping and couldn't support as much life as it used to be able to, so the sliver of the population left behind to die on the now desert world of Vulcan were the Surak worshipping Vulcans.
2000 years before the invention of replicators.
Hell, if you go by TOS, when the Romulans first met Humanity, in the 22nd century, they hadn't invented warp Drive yet... So 18 centuries earlier the Romulans must have colonized world after world in impulse powered generational ships, where it took them decades to slip between worlds instead of days, this is not a lifeplan some one with choices sets out on.
If the Saurakian Vulcans won the age of enlightenment, they might have forced/only allowed the the Romulan refugees to use the highly irradiated metal from the bombsites to build their massive space arks. I mean that shit had to be cleared and it was valueless and poison, it would have fucked up the planet if it wasn't kicked off the planet screwing up the water table and food chain for more generations than it should have since they had the technology, if not the will to clean it all up or eject it into space... Which explains the forehead mutations.
The space arks were toxically irradiated.
Either the Romulans didn't have a choice or the Saurakian Vulcans were assholes still trying to kill the Romulans with "kindness" like the yanks did with those smallpox blankets to the Indians.