Freeman J. Dyson (again)

"The technologies which have had the most profound effects on human life are usually simple." A good example is hay - cutting grass in autumn to keep animals alive during the winter - unknown to the Roman Empire where grass grew year around. "According to the Hay Theory of History, the invention of hay was the decisive event which moved the center of gravity of urban civilization from the Mediterranean to Northern and Western Europe."
(from his book "Infinite in All Directions")