Inside Russia, that force comes with repression against dissidents and civil rights that only accelerated during the distraction of the Sochi Olympics. Abroad, force in the form of military action, trade sanctions or natural-gas extortion is applied wherever Mr. Putin thinks he can get away with it.

On Monday, the markets plummeted in response to the news that Russia had invaded a European nation. Just a few days later, as cautious statements emanated from the White House and the European Union, most markets had rebounded fully. This was due to an illusion of a resolution, as if it matters little to the fate of the global economy that a huge nuclear power can casually snap off a piece of a neighboring country.

Thanks to their unfettered access to Western markets, Mr. Putin and his gang have exploited Western engagement with Russia in a way that the Soviet Union’s leaders never dreamed of. But this also means that they are vulnerable in a way the Soviets were not. If the West punishes Russia with sanctions and a trade war, that might be effective eventually, but it would also be cruel to the 140 million Russians who live under Mr. Putin’s rule. And it would be unnecessary. Instead, sanction the 140 oligarchs who would dump Mr. Putin in the trash tomorrow if he cannot protect their assets abroad. Target their visas, their mansions and IPOs in London, their yachts and Swiss bank accounts. Use banks, not tanks. Thursday, the U.S. announced such sanctions, but they must be matched by the European Union to be truly effective. Otherwise, Wall Street’s loss is London’s gain, and Mr. Putin’s divide-and-conquer tactics work again.