A 19-year-old Ukrainian nationalist from a remote farming village, raised on stories of his family’s suffering during Stalin’s great engineered famine, embittered by Moscow’s long imperialist dominion, enraged by the slaying of a fellow student in Kiev during the uprising of 2014, convinced any price is worth paying to stop the Russian annexation of Crimea, takes the long road to Sevastopol.

He is a simple angular man, a dreamer, who as a young boy had engraved his initials on a retaining wall of rocks at the back of his family’s plot. When asked why, he replied, “Because one day people will know my name.”

On the farm, he works hard by day and reads voraciously by night. He is consumed with the long suffering of the Ukrainian peasant laboring in near feudal conditions. Neighboring countries have gained their independence and dignity after Soviet occupation. Why, he asks, should Ukraine not do the same?

To this teenager, the issue is simple. The imperial ruler in the Kremlin knows nothing of Ukraine. The 21st-century world is changing, but this high officer of the imperium is determined to wind back the clock to the 20th. A good student, the man travels to Kiev, where an older brother works. He falls into the “Young Ukraine” movement, a radical student circle in which feelings run high over the shotgun referendum that saw the people of Crimea vote with Orwellian unanimity for union with Russia. At night, he fingers the hand-engraved Browning pistol that was once his father’s.

A plot is hatched. The Russian defense minister is to visit Sevastopol with his wife to celebrate the wise choice of the Crimean people and speak of Russia’s civilizing influence over this beautiful but backward region. Fanfare follows. “Wide Is My Motherland” booms from loudspeakers as the minister’s procession of black limousines snakes along the waterfront. The assassin is waiting at a point where the minister and his wife are to greet local dignitaries.

Two shots ring out. One cuts through the minister’s jugular vein. The other penetrates his wife’s abdomen. The minister’s last words are spoken to her: “Don’t die, don’t die, live for our children.”

Events now move quickly. Russia annexes Crimea. It declares war on Ukraine, takes Donetsk in short order, and annexes the eastern half of the country. The United States warns Russia not to advance on Kiev. It reminds the Kremlin of America’s binding alliance with Baltic states that are NATO members. European nations mobilize.

Desperate diplomacy unravels. A Ukrainian counterattack flounders but inflicts heavy casualties, prompting a Russian advance on the capital. Two NATO F-16s are shot down during a reconnaissance flight close to the Lithuanian-Russian border. Russia declares war on Estonia, Latvia and Lithuania. Invoking Article 5 of the North Atlantic Treaty — an attack against one member shall be considered an attack against all — the United States and its European allies come to their defense. China, in what it calls a pre-emptive strike, invades Taiwan, “a potential Crimea.” Japan and India declare war on China. World War III has begun.

It could not happen. Of course, it could not happen. The institutions and alliances of a connected world ensure the worst cannot happen again. The price would be too high, no less than nuclear annihilation. Civilization is strong, humanity wise, safeguards secure.

Yes, the Great War, the end of empires and the old order, was triggered by a teenager. And, as Butcher writes, “It was out of this turbulent collapse that Bolshevism, socialism, fascism and other radical political currents took root.” They would lead to World War II.

Princip acted with a small group of accomplices bent on securing the freedom of the south Slavs from the Austro-Hungarian Empire. Luck helped him, diplomatic ineptitude force-multiplied his deed, and by the age of 23 this farmboy whose name would be remembered was dead of tuberculosis in a Habsburg military prison.

Then, too, exactly a century ago, it could not happen. The world had finessed other moments of tension. Yet very quickly Austria-Hungary had declared war on Serbia, prompting Russia to mobilize in defense of Belgrade, prompting the Kaiser’s Germany to attack France pre-emptively and Britain to declare war on Germany. The war haunts us still.

The unthinkable is thinkable. Indeed, it must be thought. Otherwise it may occur — soldiers reduced, in Butcher’s words, to “fodder locked in the same murderous morass, sharing the same attrition of bullet and barrage, disease and deprivation, torment and terror.”