Did some evening courses on history and one of the professors was on the cutting edge climate history (Fredrik Charpentier Ljungqvist). Most of his books are only available in Swedish but if you're interested in climate history then he contributed to an anthology called "Nordic Climate Histories". Most of Sweden used to be plains with a lot of cattle, but it collapsed somewhere before the 'Migration Period' and the landscape became covered in forests instead. Anyway, Finland is notable for being area where people became settled farmers with the worst circumstances for farming in the world. Why they decided to become farmers is kind of baffling to historians. Just Sisu and stubbornness? Who knows.

And most societies, before steam trains, were tied together via sea/river routes. Look at the Mediterranean for example, Carthage makes a lot more sense if you consider that it was easier to go from Tunisia to Sardinia than to go 100 miles inland.