Comment by Gravityloss

Might be because of land travel in those days. I wonder how besides the large scale geography like mountains, the smaller scale and biotopes also affected it. Open farmland or steppes are different to travel than dense forests or cliffs. Even today, trade by land is still more constrained than by water, if you look at large container ships vs trains, and where most GDP is concentrated. Thomas Pueyol makes some nice twitter threads about this, how geography has shaped history. Of course simplified and with a chosen narrative, but something that the typical "great man theory of history" doesn't do.