Seeking meaning in the stories they tell, historians are inclined to look for deeply rooted or underlying causes for the events they recount. And yet, is it possible that, at least on occasion, historical change derives less from profound and long-term sources than from coincidence, chance, or the decisions of a few that might well have gone another way?

Consider, for example, the problem of explaining the rise of Europe to a position of global power in the modern era. What if the Great Khan Ogodei had not died in 1241, requiring the Mongol forces then poised for an assault on Germany to return to Mongolia? It is surely possible that Central and Western Europe might have been overrun by Mongol armies as so many other civilizations had been, a prospect that could have drastically altered the trajectory of European history. Or what if the Chinese had decided in 1433 to continue their huge maritime expeditions, creating an empire in the Indian Ocean basin and perhaps moving on to “discover” the Americas and Europe? Such a scenario suggests a wholly different future for world history than the one that in fact occurred. Or what if the forces of the Ottoman Empire had taken the besieged city of Vienna in 1529? Might they then have incorporated even larger parts of Europe into their expanding domain, requiring a halt to Europe’s overseas empire-building enterprise?

None of this necessarily means that the rise of Europe was merely a fluke or an accident of history, but it does raise the issue of “contingency,” the role of unforeseen or small events in the unfolding of the human story. An occasional “what if” approach to history reminds us that alternative possibilities existed in the past and that the only certainty about the future is that we will be surprised.