You never know with history because it's not possible to conduct experiments. However, I'm very sceptical of arguments about the lasting effect of volcanic erup

You never know with history because it's not possible to conduct experiments. However, I'm very sceptical of arguments about the lasting effect of volcanic eruptions on world history during the last 2000 years. Known eruptions last 2-3 years, which is bad but of limited duration. [1] Pandemics and disease in general have had far greater impact on humans. The Bubonic Plague epidemic of 1348-1350 wiped out at least 1/3 of the population of Europe according to reputable sources. [2] It affected medieval societies for decades by changing the cost and availability of labor. Destructive wars like the 30 Years War had effects of similar magnitude. (This relevant for the Roman Empire, which suffered continuous invasions starting from 406AD onwards in the West.) [1] https://en.wikipedia.org/wiki/Year_Without_a_Summer https://en.wikipedia.org/wiki/Year_Without_a_Summer [2] https://en.wikipedia.org/wiki/Black_Death https://en.wikipedia.org/wiki/Black_Death