Last month, I traveled to Vienna, the former seat of the Austro-Hungarian Empire and a fitting place to contemplate the approaching 100th anniversary of the conclusion of World War I.

That conflict began with Austria-Hungary’s declaration of war against Serbia in July 1914, following the assassination of Austro-Hungarian archduke Franz Ferdinand. It ultimately led to more than 15 million deaths, the collapse of four empires, the rise of communism and fascism in some of Europe’s leading states, the emergence and subsequent retreat of America as a global power, and other developments that profoundly altered the course of the 20th century.

World War I was “the deluge … a convulsion of nature,” remarked Britain’s Minister of Munitions David Lloyd George, “an earthquake which is upheaving the very rocks of European life.” Although that conflict ended a century ago, it still offers three crucial lessons that are relevant to our increasingly disordered world today.

First, peace is always more fragile than it seems. In 1914, Europe had not experienced an all-out, continental conflict since the end of the Napoleonic wars a century earlier. Some observers believed that a return to such catastrophic bloodletting had become almost impossible. The British author Norman Angell would immortalize himself by suggesting, just a few years before World War I, that what we would now call globalization had rendered great-power conflict obsolete. War, he argued, had become futile because peace and the growing economic and financial linkages between the major European states were producing so much prosperity.

Angell had good company in the multitude of thinkers who believed that improved communications were knitting humanity ever more tightly together, that international arbitration was making war unnecessary and that nationalism was being suppressed by newer, more enlightened ideologies and improved forms of international cooperation.

The eruption of World War I showed that these trends were no guarantee of peace at all, because they were so easily overtaken by the darker forces of conflict and rivalry. Destabilizing shifts in the balance of power, the geopolitical rigidities created by hair-trigger military plans, the rise of social Darwinist and militarist ideas that exalted the role of war in human and national development, and the tensions surrounding a rising Germany’s bid for European preeminence and world power had created a great mass of combustible material that was set alight by the seemingly minor spark provided by an archduke’s assassination.

If we assume today that war between the great powers cannot happen — that economic interdependence will automatically hold rising tensions between the United States and China in check, that advances in human enlightenment will consign nationalism and aggression to the pages of history — then we, too, risk discovering that our own peace is far more precarious than we think.

Second, World War I reminds us that when peace gives way and international order collapses, the consequences can be far worse than almost anyone imagines. Even after World War I erupted, many observers believed that its duration would be brief and its effects limited. In September 1914, the Economist assured its readers of “the economic and financial impossibility of carrying out hostilities many more months on the present scale.” Yet this prediction, like so many others, was badly wrong, because the very sources of progress that had created so much optimism in the years before the war now made its impact all the more cataclysmic.

The development of more modern, capable states in the decades before World War I now provided Europe’s rulers with the ability to tax and conscript their populations more efficiently and otherwise sustain a horrendous conflict far longer than expected. The industrial and technological breakthroughs of the age now allowed killing on an industrial scale. As the rector of one British church observed, “All the resources of science had been called upon to perfect weapons of destruction for mankind.”

As the conflict dragged on, ethical prohibitions eroded and dreadful innovations such as aerial bombing, poison gas and unrestricted submarine warfare were introduced; the war precipitated the genocide of the Armenians and countless other crimes against noncombatants. The long-term ramifications were equally traumatic, as World War I remade the political map of continents, set off revolutions from the heart of Europe to the Far East, and incubated some of the most poisonous political ideologies in human history.

World War I was not so different, in this respect, from so many of the great-power wars that have periodically ruptured the international system. Once the existing order collapses, there is no telling how far the destruction, the transgressions of accepted morality, and the geopolitical upheaval will go. As Americans consider how strongly — or even whether — to defend the international order their country created against the growing pressures exerted by authoritarian revisionist powers such as China and Russia, this lesson is worth keeping in mind.

So is a third lesson: that when the U.S. pulls back from the world, it may well end up reengaging later at a much higher cost. America played a key role in the economic rehabilitation of postwar Europe during the 1920s. Yet it rejected the sort of long-term strategic and military commitments it would eventually make after World War II.

Americans did so for reasons that seemed quite understandable at the time. There was widespread reluctance to abrogate the tradition of non-entanglement in Europe, as well as fear that membership in the League of Nations would undermine U.S. sovereignty and usurp Congress’s constitutional prerogatives with respect to declaring war. Most of all, there was strategic complacency brought on because the defeat of Germany and its allies seemed to have banished significant geopolitical dangers far over the horizon.

The history of the 1930s and 1940s soon demonstrated, however, that new and even greater dangers could arise absent timely, determined efforts by the democracies to stop them. Although the U.S. and its allies eventually succeeded in defeating the Axis powers during World War II, they were able to do so only at a cost in lives, treasure and overall devastation that dwarfed the toll inflicted by World War I.

This is why the U.S. chose to stay so deeply engaged in the affairs of Europe, the Asia-Pacific and other key regions after 1945: Because American officials had learned that in geopolitics as in medicine, prevention is often cheaper than cure. At a moment when the future of America’s commitment to international leadership is once again in question, this is perhaps the most important insight World War I has to offer. And there are far worse ways to remind oneself of that insight than by walking through Vienna, a city full of monuments to an empire — and an international system — that World War I brought crashing down.

Bloomberg Opinion columnist Hal Brands is the Henry Kissinger Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies and the co-author of “The Lessons of Tragedy: Statecraft and World Order.”.

In a time of both misinformation and too much information, quality journalism is more crucial than ever.
By subscribing, you can help us get the story right.