If historians don’t try to explain why the world has turned out the way it has, they are falling down on the job. Yet academic historians often have trouble seeing the forest for the many trees of highly specialized research. Even more worryingly, many of them have increasingly retreated from questions of causation, at the same time as their colleagues in the social sciences have been devising ever more sophisticated techniques for addressing precisely such questions.My project runs counter to these trends. I am convinced that big questions are very much worth asking and that we need to employ a wide variety of methods and approaches to tackle them. Throughout my book, I draw on a rich body of scholarship produced by economists, political scientists, and sociologists who have been interested in the origins of what is known as the “Great Divergence,” Europe’s (or the “West’s”) pulling ahead of other parts of the world during the last few centuries. Transdisciplinary connections are essential in addressing big questions such as this one, and I seek to demonstrate how much historians stand to profit from this openness.My book takes the globalization of history seriously: we simply cannot hope to make sense of one particular case without looking at many others as well. My perspective is resolutely comparative. If we want to understand why large-scale empires never returned to much of Europe, we need to understand which factors were responsible for their resilience elsewhere. In arguing that the absence of such empires was beneficial to certain kinds of human flourishing, I have to show how and why their presence thwarted progress.I also keep asking how robust these outcomes were. How readily might history have turned out very differently? This question requires me to turn to counterfactuals, to ask how much would have had to be different for broad trajectories of development to change. Historians are sadly resistant to this way of thinking. In my book, I hope to show that counterfactual reasoning not only makes sense but that it can be of great value in illuminating the overall contours of historical change. I find that Europe never again came close to being ruled by a single empire.Finally, I make sure to relate historical processes to the physical environment. Geography and ecology have long shaped historical trends and need to be incorporated into our analyses. In my book, I identify a number of environmental features that facilitated the formation of large imperial states in some parts of the world but made it harder in others, above all in Western Europe: the intersection of land and sea, the distribution of mountain ranges and large flood plains, and the role of the steppe in supporting mobile challengers to sedentary societies.