In the seventeenth and eighteenth centuries the agrarian empires—above all, Romanov Russia and Qing China—effectively killed one of the horsemen of the apocalypse. Because of this, the pressure of social development against the hard ceiling did not trigger waves of steppe migration the way it had done in the second and twelfth centuries; and because of that, it seems, even the combined weight of state failure, famine, disease, and climate change was not enough to drive the cores into collapse. The steppe highway had been closed, and with it closed an entire chapter of Old World history.
