It is always a good idea to start at the end. The epilogue of my book takes its cue from the famous question in the Monty Python movie The Life of Brian: “What have the Romans ever done for us?” It is true that the standard answer—that the Roman Empire brought peace alongside various material fruits of civilization from roads to wine—holds up well: never again would so much of Europe be at peace for such a long time.But that peace was bought a price. Stable empire ushered in conservatism and stagnation. As impressive as Roman ruins still look to us today, the Roman economy failed to deliver sustainable growth. After accelerating among the ancient Greeks, scientific discovery and technological advances stalled under Roman rule. Democracy, another Greek experiment, was snuffed out. Later on, the Roman authorities sought first to suppress and then to co-opt Christianity, which had emerged independently from established power structures.It was only by falling apart during the fifth, sixth, and seventh centuries AD that the Roman Empire finally performed its most important service to human development: to go away for good. By setting Europe free from the conventional strictures of imperial control, Rome’s demise ushered in an age of fracture and experimentation that would eventually change the whole world.At the very end I return one more time to counterfactuals by asking, what if there had never been a Roman Empire to begin with? How would that have affected Europe’s journey toward modernity? Rome’s cultural legacy lent some degree of unity of medieval and early modern Europe that would otherwise have been missing. This promoted the flow of people, goods, capital, and ideas across borders.I argue that Christianity was probably the single most influential legacy of Rome. While it helped pull medieval societies together, it deepened divisions later on. The Protestant societies of northwestern Europe were the main beneficiaries and played a key role in bringing about unprecedented change.My book serves as a reminder that continuities must not be overrated; sometimes breakages were more important. We tend to place a lot of emphasis on the continuities of the Roman tradition, from Romance languages to the calendar. Yet it was a glaring absence that mattered most, something that did not happen in Europe even though it routinely occurred elsewhere: the return of large-scale empire. This shows that crises can be a blessing in disguise. While it must have been hard to live through the unraveling of the Roman Empire, its long-term consequences yielded benefits that had been truly unimaginable. The lesson is simple: the status quo isn’t always worth preserving no matter how glittering its façade.History is infinitely rich, and nobody can hope to master all its details. Nevertheless, it is possible to get a handle on its daunting complexity by tracking the roots of big changes. I already mentioned the common inability of seeing the forest for the trees. In this case, the many competing explanations of the “Great Divergence” are the trees; the fall of Rome and the failure of anything like it to re-appear are the forest—the environment that shaped development in Europe for fifty generations. China, India, and the Middle East inhabited different forests, and outcomes differed accordingly. It is only by operating at a high level of analytical abstraction that we are able to cut through the noise of historical events and fashion an account that makes sense of broader trends.Last but not least, I want readers to appreciate that in order to understand something that happened only once—such as the transition to modernity—it is not enough to unearth the roots of that development. We also need to understand why it did not happen somewhere else instead. This need is particularly urgent when we seek to explain the origins of modernity in European societies—an issue that has long been tainted by Eurocentric and sometimes racist notions of “Western” exceptionalism.Yet the best answer to the question of why some European societies acquired the means of pulling ahead of the rest of the world and of changing it in the process turns out to be quite straightforward. By maturing under institutional and environmental conditions that were sufficiently different from those that prevailed elsewhere, these societies ended up being better at nurturing economic development, building up the stock of useful knowledge, and dominating others.For good or ill, all these expanding capabilities were closely and inextricably intertwined. This may come as a disappointment to steadfast admirers of the glories of “Western Civilization” and to vocal critics of its enduring legacy of exploitation, global inequality, and environmental degradation. But that has been the course of history. It is up to us to grapple with the consequences.