Climate shocks, dynastic cycles, and nomadic conquests
Nomadic conquests have helped shape world history. We may indulge ourselves for a moment to imagine the following counterfactuals: What if Western Europe did not fall to seminomadic Germanic tribes, or Western Europe was conquered by the Huns, Arabs, or Mongols, or Kievan Rus did not succumb to Mongolian invaders, or Ming China did not give way to the Manchu Qing?