When the era of Communist rule began in Russia in 1917, religion was seen as a hindrance to a thriving socialist society. As Karl Marx, coauthor of the The Communist Manifesto, declared, “Communism begins where atheism begins.”

Joseph Stalin, as the second leader of the Soviet Union, tried to enforce militant atheism on the republic. The new “socialist man,” Stalin argued, was an atheist one, free of the religious chains that had helped to bind him to class oppression. From 1928 until World War II, when some restrictions were relaxed, the totalitarian dictator shuttered churches, synagogues and mosques and ordered the killing and imprisonment of thousands of religious leaders in an effort to eliminate even the concept of God.

“He saw this as a way of getting rid of a past that was holding people back, and marching towards the future of science and progress,” says the historian Steven Merritt Miner, author of Stalin's Holy War: Religion, Nationalism, and Alliance Politics. “Like most of what Stalin did, he accelerated the violence of the Leninist period.”

On a personal level, Stalin was well-acquainted with the church. As a young man in his native Georgia, he had been first expelled from one seminary and then forced to leave another, after he was arrested for possessing illegal literature. As the young seminarian grew increasingly disillusioned with religion, “the all-encompassing nature of Marxism, almost religious in its universality, was tremendously appealing,” writes Oleg V. Khlevniuk, in his 2015 biography of the dictator.

That all of human history had been leading up to the “higher stages” of socialism was a seductive prospect, and one that “endowed the revolutionary struggle with special meaning,” he writes. By this view, the end more than justified even the most extreme means.

By the time Stalin came to the height of his power, in the 1920s, the Russian Orthodox Church remained a powerful force, despite more than a decade of anti-religious measures under Vladimir Lenin. Russia’s peasants were as faithful as ever, writes Richard Madsen in the Oxford Handbook of the History of Communism, with “the liturgy of the church” still “deeply embedded in [their] way of life,” and “indispensable for their sense of meaning and community.” A powerful church was a risky prospect, and one that might threaten the success of the revolution.

The “Godless Five-Year Plan,” launched in 1928, gave local cells of the anti-religious organization, League of Militant Atheists, new tools to disestablish religion. Churches were closed and stripped of their property, as well as any educational or welfare activities that went beyond simple liturgy.

Leaders of the church were imprisoned and sometimes executed, on the grounds of being anti-revolution. The few clergy who remained were replaced by those deemed to be sympathetic to the regime, rendering the church still more toothless as a possible focal point for dissent or counter-revolution.

There was a relatively simple idea at its heart of this plan, explains Madsen: It was possible and desirable to eradicate “traditional national consciousness,” in order to “create a society based on the universal principles of socialism.” More than that, the steps were replicable: The plan was eventually exported to other communist countries that had chosen to ally themselves with the USSR.

On the ground, social reforms and pro-atheism publications sought to eliminate religion from day-to-day life altogether. Launched in 1929, the new Soviet calendar initially featured a five-day continuous week, designed to do away with weekends and so revolutionize the concept of labor. But it had a secondary function: By eliminating Fridays, Saturdays, and Sundays, the days of worship for Muslims, Jews and Christians, the new calendar was supposed to render observance more trouble than it was worth.

At the same time, the sacked churches, synagogues and mosques were transformed into anti-religious “museums of atheism,” where dioramas of clerical cruelty sat alongside crisp explanations of scientific phenomena. Icons and relics, meanwhile, were stripped of their mystique and treated as ordinary objects. The general public didn’t seem to have been especially swayed by these exhibits—though they enjoyed the attractions themselves. The most popular of these museums remained open as late as the 1980s, the New York Times reported..

All the while, the nominally independent League of Militant Atheists disseminated anti-religious publications, organized lectures and demonstrations, and helped atheist propaganda work its way into almost every element of socialist life. The popularity of these publications didn’t always indicate that atheism was winning out, says Miner: “Some believers bought atheist publications because that was when they found out about what was going on.”

By 1939, barely 200 churches remained open, out of about 46,000 before the Russian Revolution. Clergy and laymen had been executed or placed in labor camps, while only four bishops remained “at liberty.”

The Orthodox church was all but vanquished, explains Madsen—until World War II. After Nazi invaders reopened churches in Ukraine to encourage sympathy from the local population, Stalin followed suit throughout the country, in a naked attempt to drum up national support for the Fatherland.

Stalin appeared to have had absolute conviction in his anti-religious war. “I have no doubt that he was a thoroughgoing atheist,” says Miner. “He just thought [religion] was stuff and nonsense, and a way to throw dust in the eyes of people so you can control them—really, that it was childish to believe something else.”

Meeting Franklin D. Roosevelt, Stalin seems to have been genuinely surprised to learn that the president attended religious services, asking the diplomat W. Averell Harriman “whether the president, being such an intelligent man, really was as religious as he appeared, or whether his professions were for political purposes.”

Even as Stalin’s measures succeeded in sucking the center out of the Russian Orthodox church, they had minimal impact on people’s actual faith. As late as 1937, a survey of the Soviet population found that 57 percent self-identified as a “religious believer.” Stalin’s central belief—that every rational person would, as Miner puts it, “naturally discard religious superstitions just as a baby outgrows its rattle”—proved misguided.

Even after World War II, the anti-religious campaign stormed on for decades, with Bibles forbidden and little to no religious education. Still, by 1987, the New York Times reported, “Soviet officials have begun to admit that they may be losing the battle against religion.”

Culturally speaking, urban Bolsheviks had had little in common with rural peasants who made up much of the general populace. For the peasants, militant atheism was never quite captivating enough to replace centuries of religious practice, especially as the memory of the 1917 revolution, and Stalin’s rule, grew increasingly dim.