One hundred and eleven years ago this past Saturday (June 28, 1914), Bosnian Serb terrorist Gavrilo Princip assassinated Franz Ferdinand, the heir to the Austro-Hungarian throne, and his wife Sophie on a street in Sarajevo. The Balkans had been the scene of wars in 1912 and 1913, as nationalist forces sought to end Ottoman rule over their people. Balkan unrest also affected Austria-Hungary, which occupied Bosnia and Herzegovina and sought to block Serbian expansion in the region.

The assassinations, which Austria-Hungary blamed on Serbia, led to an ultimatum being delivered to the Serbian foreign minster on July 23, 1914. The Serbs accepted all the terms of the ultimatum except one: they refused to allow Austria-Hungary to participate in an internal inquiry into the assassination. Serbia appealed to Russia for help, while Austria-Hungary sought Germany’s support. Militaries on both sides were mobilized.

On July 28, 1914, one month after the assassinations, Austria-Hungary declared war on Serbia. Four days later, Germany declared war on Russia, and two days later Germany declared war on France, who was allied with Russia. And one day after that, England declared war on Germany. Bismarck’s prediction that “some damn fool thing in the Balkans” would ignite the next great European war came true.

The seeds of the First World War — what an earlier generation called the Great War — were planted in the mid-to-late 19th century when Bismarck’s Prussia waged three wars to unify Germany. The last of those wars — known as the Franco-Prussian War — left geopolitical scars that would not heal. Bismarck’s skillful diplomacy after the war kept the general peace, but the great Prussian statesman left the scene in 1890, forced out of office by Kaiser Wilhelm II, whose policies combined with Franco-Russian diplomacy succeeded in unraveling what George F. Kennan called “Bismarck’s European order.”

Kennan’s two books on Europe’s diplomacy at the end of the 19th century and his lectures on World War I collected in his book American Diplomacy should be required reading by today’s diplomats and statesmen. In The Decline of Bismarck’s European Order, Kennan wrote that he came to see the First World War “as the great seminal catastrophe” of the 20th century, and that it “lay at the heart of the failure and decline of … Western civilization.”

In that book, Kennan focused on Franco-German relations between 1875 and 1890. He praised Bismarck’s “treaty structure of the 1880s,” which he noted was “designed to keep peace between the Austrians and the Russians, to make it clear that neither could expect German help in an effort to attack the other, but also to assure that neither of them would become an ally of the French in an aggressive war of revenge against Germany.”

In The Fateful Alliance, essentially a sequel to The Decline of Bismarck’s European Order, Kennan recounted the slow emergence of the 1894 Franco-Russian alliance that upset Bismarck’s European order and set the stage for the entangling alliances that were propelled toward war by the assassination on June 28, 1914.

In American Diplomacy, Kennan called the First World War the “forgotten factor,” and noted that “all the lines of inquiry … lead back to it.” He is surely right about that. The events set in motion by Princip’s assassinations shaped the rest of the 20th century and continue to shape events in this century.

The consequences of World War I include the rise of communism and Nazism to state power, the geopolitical rivalries of the modern Middle East, the Second World War (which to a large extent was a continuation of the First World War), the 45-year Cold War that emerged from the ashes of the Second World War, the emergence of the nuclear age, the end of colonialism, and so much more. In the television documentary The Great War and the Shaping of the 20th Century, the narrator notes that World War I “colored everything that came before and shadowed everything that followed.”

At the end of The Fateful Alliance, Kennan, sounding like George Washington in the Farewell Address and John Quincy Adams in the early 1820s, wrote that “[t]he relations among nations, in this imperfect world, constitute a fluid substance, always in motion, changing subtly from day to day in ways that are difficult to detect from the myopia of the passing moment, and even difficult to discern from the perspective of the future one.”

Kennan counseled, therefore, that “wise and experienced statesmen usually shy away from commitments likely to constitute limitations on a government’s behavior at unknown dates in the future in the face of unpredictable situations.” These are among the important lessons of the First World War. We neglect them at our peril.

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