I had a classics and Roman history professor who used to say that there is a misconception about separation, that the pre-iron age societies we look at now only appeared to be unconnected. ‘The illusion of separation’ was his term. Largely proven now of course but when he was coming up there were stil very clear borders.

One of the examples that I remember the best is about the supply of wheat, that if there was a blight on the crop in Egypt, the shortage would be felt as far away as the Indus and Central Europe.

There might be something to a theory of the inverse leading to the Bronze Age collapse. Lacking the means to feed themselves in a harsher north, people follow supply lines south to the Mediterranean, taking to raiding and piracy to survive. The same can be said for how the Balkans were later settled from the south.