THE fall of an autocrat leads to foreign occupation and civil war. A revolutionary movement with a messianic vision capitalizes on the chaos to gain power. The revolutionaries rule through terror and the promise of utopia, and inspire copycats around the world. But other nations impose a quarantine, internal rivals regain ground, and despite initial successes the new regime seems unlikely to survive — especially once outside powers, including the United States, join the fight against it.

This is the story to date of the Islamic State, which defied predictions of its imminent collapse by capturing Ramadi in Iraq and Palmyra in Syria last week. A “tactical setback,” President Obama called these developments, and quite possibly they are; it’s still hard to imagine that the self-styled caliphate can long endure.

But this is also the story of the Soviet Union’s early days, when it seemed highly implausible that a cabal of Bolsheviks would rule the Russian empire for seventy-odd years. When the Bolshevik regime was about the age that the Islamic State is today, the United States, France, and Britain were supporting its White Russian adversaries and landing troops in Russia; Japan and a reborn Poland were pressuring the Bolsheviks from east and west; and the fear instilled by the Red Terror seemed like the primary force keeping the pariah state from crumbling.

A generation later, that pariah was a global superpower.

The differences between the two situations are legion, of course. The Bolsheviks controlled key urban and industrial centers, while ISIS is truly dominant only in the Iraqi and Syrian hinterland. The Soviet Union’s foreign enemies were exhausted by world war, and their ability to project military power was far more limited than America’s is today. However geopolitically important, Russia in 1919 was peripheral to many great powers’ immediate security concerns, while ISIS is sitting at an oil-rich crossroads and murdering Western citizens every chance it gets. And the Islamic State’s worldview conspicuously (and mercifully) lacks the Western cheering section and sense of historical momentum that Marxist-Leninism once enjoyed.