I like your concise, to-the-point post-natural climate changes, and the effect they would have on travel and trade with distant places are ignored by a lot of those in the field of archaeology.
If a relatively small volcanic eruption in Iceland shuts down air travel in today’s world, it isn’t really that difficult to imagine what havoc a tsunami, lava flow, rain of ash-or just a Siberian express weather event-would cause, possibly shutting down ocean and land travel and trade in some areas for awhile, never mind something major. We know that Greenland was green about 1000 years ago, and there were grapes grown and wine made in Britain...
Thanks for the kind remarks.
In the ancient world there was a sort of pulse of migration down the steppes; each time the result was a movement of large groups of people into Europe, India, and even into China. The sudden failure of agriculture due to the weather changes even led to starvation, susceptibility to epidemics, and vulnerability to the ingress of other groups.
In Scandinavia the Medieval Warming — an entirely natural event — led to cultivation at higher latitudes and altitudes than are possible to this day. This is attested by ruined farmsteads for example. There was a population boom that went on generations and changed Europe.
These cycles had an impact on minor organizations (/s) like the Roman Empire, which ultimately had a population loss and economic downturn right at the time large groups started into Europe again. The previous big ingress led to the arrival of the Scythians.