For (its) political diversity Europe had largely to thank its geography. There were no enormous plains over which an empire of horsemen could pose its swift domination; nor were there broad and fertile river zones like those around the Ganges, Nile, Tigris and Euphrates, Yellow and Yangtze, providing the food for masses of toiling and easily conquered peasants. Europe's landscape was much more fractured, with mountain ranges and large forests separating the scattered population centres in the valleys' and its climate altered considerably from north to south and west to east...

Europe's differentiated climate led to different products, suitable for exchange; and in time, as market relations were developed, they were transported along the rivers or the pathways which cut through the forest between one area of settlement and the next...Here again geography played a crucial role, for water transport of these goods was so much more economical and Europe possessed so many navigable rivers.

Paul Kennedy, The Rise and Fall of Great Powers, 1987

Jared Diamond, Guns, Germs and Steel