They have postulated that the volcano created a nuclear winter scenario which dropped temperatures worldwide which caused crop failures in Europe and the Mediterranean which caused famine which caused disruption in the food chain which caused famine to spread which compromised people's ability to fight disease which assisited the spread of the plague. Remove those two events from history and imagine what might exist today.
Duane
Humans thrive during natural warm cycles and die in large numbers during cold cycles.
The Roman Empire coincided with a natural warm cycle several degrees warmer than the 20th Century. It was probably about as hot as the "disaster" we were threatened with by "global warming" alarmists.
The Roman Empire ended during a significant drop in global temperatures that lasted a few hundred years. Blaming it on this volcano or that volcano ignores the huge hot object in our sky that keeps our planet warm. Variations in solar output have far more effects on the earth temperature than anything else. Deaths are often blamed on famine and or some disease, both of which are the result of global cooling.
There was a medieval warm period during which most of Europe did well, and so did so-called Vikings from north lands that prospered during warm the warm period. Populations across Europe and Asia greatly increased.
Then there was what is called the "little ice age" which lasted from the 15th century until the 18th century. Global temperatures dropped. Widespread famine killed many across Europe. Starving people are much more susceptible to disease so the plague found easy target. The British quit being wine merchants and became brewers of beer.
The little ice age ended about the 19th century and warm continues today, although we may be seeing an end of the warm times. Scientists write papers alleging causes such as volcanoes and such. Human activity always gets blamed, witches, corporations, whatever scapegoat they can point to. Most probably its the sun that causes it all and none of the scapegoats have ever been responsible for any of it.
We should all be hoping for global warming because humans always thrive, but unfortunately we or our children are more likely to see famine and disease caused by a solar cooling cycle.
Bob