If a Volcano Killed Rome Instead of the Barbarians

Question

In the fourth and fifth centuries AD, the Roman Empire had fallen under bad times. Within its boundaries, the once powerful nation had been getting compromised by political corruption and civil unrest. The final straw were countless barbarian invasions, most notably one led by the Gothic warlord Alaric, who succeeded in breaching the city's gates and sacking the city of Rome. From there, Europe underwent a period of cultural stagnation and unrelenting war, a period stereotypically known as "The Dark Ages", before germinating into the Middle Ages which would blossom into the Renaissance and the Enlightenment.

But in this alternate scenario, the final nail in the coffin of Rome wasn't wave after wave of Eurasian tribesmen, but a volcanic winter coming from the likes of either of these choices:

• Yellowstone
• Toba
• Campi Flagrei

Considering that each of the three volcanoes had different chemistries and compositions, would the timeline of the Dark Ages and the Middle Ages be identical, or would the really bad weather change every aspect of European history?

Answer 1

There seems to still be a fair amount of debate on just how severe the global effects of a super volcano eruption were historically or would be now. The greatest devastation is always localized, so the locations of your three choices matter quite a bit.

Yellowstone

A Yellowstone eruption, from the perspective of the Europeans, would most likely take the form of a few years of colder weather and low-yield harvests. This would certainly have an impact in the short term with some starvation and a greater tendency toward uprising, barbarian movement, or chaos, but the long term effects wouldn’t be too serious. North America and its inhabitants would experience some devastation, possibly leading to forced migrations southward. Thus the biggest difference would come during the age of exploration, when Europeans might find far fewer Native Americans occupying North America.

Toba

Toba’s distance from Europe is also substantial enough to lessen the direct impact of the explosion, but its proximity to Asia might have interesting effects. Similarly to Yellowstone, Europeans would probably experience several years — maybe even a decade or two — of much colder weather, but it’s unclear how severe it would be. Starvation and increased disorder would happen, but it’s hard to know how much it would affect Europe long term. What might happen, however, is a much earlier migration from Asia into Europe. If Toba’s local effects are devastating enough, you might see eastern invasions happening much sooner, possibly with great long-term consequences.

Campi Flagrei

Campi Flagrei seems to have less historically documented destructive power than the other two, but it’s definitely a more local threat. If it were to experience an eruption on the level of Toba or Yellowstone, you could feasibly see devastation on the continent. With severe ash fall throughout Europe and severe damage in Italy, there might not be a Rome left to sack. Now you might see migrations out of Europe, perhaps east into Asia and the Middle East or south into Africa. This would fundamentally reshape Europe for the rest of history, but how the changes look is really up to you.