East-West divisions ease the migration of agricultural practises, because they follow the latitude, and thus remain in largely the same climate, whereas North-South migration forces the migrants to cross latitudes, potentially moving them into a different climate belt that renders their crops unfavourable.

The South and Central American cultures had barely five centuries from the first systematic agriculture until they came into contact with comparatively high-tech European culture - with all the predictably nasty outcomes we know. The Europeans had about five millenia of agricultural societies under their belts.

But of course, the convoluted European coastline probably did play a role in making marine transportation so dominant in European culture.

- Jake

Ceterum censeo Chicago esse delendam