What is less widely understood is that they have also transformed politics. A zero-sum economy leads, inevitably, to repression at home and plunder abroad. In traditional agrarian societies the surpluses extracted from the vast majority of peasants supported the relatively luxurious lifestyles of military, bureaucratic and noble elites. The only way to increase the prosperity of an entire people was to steal from another one. Some peoples made almost a business out of such plunder: The Roman republic was one example; the nomads of the Eurasian steppes, who reached their apogee of success under Genghis Khan and his successors, were another. The European conquerors of the 16th to 18th centuries were, arguably, a third. In a world of stagnant living standards the gains of one group came at the expense of equal, if not still bigger, losses for others. This, then, was a world of savage repression and brutal predation.
It's always been my impression that liberals view an economy as a zero sum game; one pie, what I don't get someone else gets. When, in fact, free markets create bigger pies for all to dig into as long as you add an ingredient.