Oxford, England — Earlier this year, I was on holiday in Corsica and wandered into the church of a tiny hamlet in the hills where I found a memorial to the dead from World War I. Out of a population that can have been no more than 150, eight young men, bearing among them only three last names, had died in that conflict. Such lists can be found all over Europe, in great cities and in small villages. Similar memorials are spread around the globe, for the Great War, as it was known before 1940, also drew soldiers from Asia, Africa and North America.

World War I still haunts us, partly because of the sheer scale of the carnage — 10 million combatants killed and many more wounded. Countless civilians lost their lives, too, whether through military action, starvation or disease. Whole empires were destroyed and societies brutalized.

But there’s another reason the war continues to haunt us: we still cannot agree on why it happened. Was it caused by the overweening ambitions of some of the men in power at the time? Kaiser Wilhelm II and his ministers, for example, wanted a greater Germany with a global reach, so they challenged the naval supremacy of Britain. Or does the explanation lie in competing ideologies? National rivalries? Or in the sheer and seemingly unstoppable momentum of militarism? As an arms race accelerated, generals and admirals made plans that became ever more aggressive as well as rigid. Did that make an explosion inevitable?

Or would it never have happened had a random event in an Austro-Hungarian backwater not lit the fuse? In the second year of the conflagration that engulfed most of Europe, a bitter joke made the rounds: “Have you seen today’s headline? ‘Archduke Found Alive: War a Mistake.”’ That is the most dispiriting explanation of all — that the war was simply a blunder that could have been avoided.

The search for explanations began almost as soon as the guns opened fire in the summer of 1914 and has never stopped. The approaching centenary should make us reflect anew on our vulnerability to human error, sudden catastrophes, and sheer accident. History, in the saying attributed to Mark Twain, never repeats itself but it rhymes. We have good reason to glance over our shoulders even as we look ahead. If we cannot determine how one of the most momentous conflicts in history happened, how can we hope to avoid another such catastrophe in the future?

Though the era just before World War I, with its gas lighting and its horse-drawn carriages, seems very far-off, it is similar to ours — often unsettlingly so — in many ways. Globalization — which we tend to think of as a modern phenomenon, created by the spread of international businesses and investment, the growth of the Internet, and the widespread migration of peoples — was also characteristic of that era. Even remote parts of the world were being linked by new means of transportation, from railways to steamships, and communication, including the telephone, telegraph and wireless.

The decades leading up to 1914 were, as now, a period of dramatic shifts and upheavals, which those who experienced them thought of as unprecedented in speed and scale. New fields of commerce and manufacture were opening up, such as the rapidly expanding chemical and electrical industries. Einstein was developing his general theory of relativity; radical new ideas like psychoanalysis were finding a following; and the roots of the predatory ideologies of fascism and Soviet Communism were taking hold.

Globalization can have the paradoxical effect of fostering intense localism and nativism, frightening people into taking refuge in small like-minded groups. Globalization also makes possible the widespread transmission of radical ideologies and the bringing together of fanatics who will stop at nothing in their quest for the perfect society. In the period before World War I, anarchists and revolutionary Socialists across Europe and North America read the same works and had the same aim: to overthrow the existing social order. The young Serbs who assassinated Archduke Franz Ferdinand of Austria at Sarajevo were inspired by Nietzsche and Bakunin, just as their Russian and French counterparts were.