Let us indulge in dark imaginings, then, in the cause of prudence. Here is one possible scenario: Clashes intensify between Ukrainian government forces and paramilitary formations organized by Russian fifth columnists. The death toll rises. The ongoing NATO dispatch of troops and F‑16s to Poland and the Baltic states, designed as a deterrence, redoubles anger in Russia—“a great and humble nation besieged,” a Russian general might declare. The American president, saying his war-weary country will not seek conflict, imposes sanctions on the entire Russian oil-and-gas sector. European states dependent on Russian energy grumble; a former German chancellor working in natural gas says his country’s interests lie with Moscow. Then, say, an independence movement of the Russian minority gains momentum in Estonia, backed with plausible deniability by Moscow’s agents, and announces support for the Donetsk People’s Republic. A wave of cyberattacks disables Estonian government facilities, and an Estonian big shot calls the Russian leader an “imperialist troglodyte trapped in a zero-sum game.” After an assassination attempt on the Estonian foreign minister at a rally in the capital, calls grow louder for the American president to invoke Article 5. He insists that “drawing red lines in the 21st century is not a useful exercise.”

The unimaginable can occur. Indeed, it has just happened in Crimea.
Let us further imagine that shortly after the president delivers his speech, in a mysterious coincidence, a Chinese ship runs aground on one of the uninhabited Senkaku Islands, administered by Japan, in the East China Sea. China dispatches a small force to what it calls the Diaoyu Islands “as a protective measure.” Japan sends four destroyers to evict the Chinese and reminds the American president that he has said the islands, located near undersea oil reserves, “fall within the scope” of the U.S.-Japan Treaty of Mutual Cooperation and Security. A Republican senator, echoing the bellicose mood in Washington, declares that “Estonia is more than a couple of rocks in the East China Sea” and demands to know whether “the United States has torn up the treaty alliances in Europe and Asia that have been the foundation of global security since 1945.” The president gives China an ultimatum to leave the Japanese islands or face a military response. He also tells Russia that another act of secessionist violence in Estonia will trigger NATO force against Russian troops massed on the Estonian border. Both warnings are ignored. Chinese and Russian leaders accuse the United States of “prolonging Cold War hostilities and alliances in pursuit of global domination.” World War III begins.