We sometimes talk about 1943 as the year that the libertarian movement really started, with the publication of three passionate books by Ayn Rand, Rose Wilder Lane, and Isabel Paterson. In his review of a new biography of Arthur Koestler, Paul Berman makes 1940 sound like a crucial year for books of liberal anti-communism (that is, of course, anti-communism by modern liberals, not classical liberals, who were always opposed to socialism). Perhaps it took 20 years for liberals and anarchists to realize what was happening in Russia and organize their thoughts about it. Libertarians got there a bit sooner, from Mises's theoretical critique in Socialism in 1922 to Rand's firsthand experiences that led to the publication of We the Living in 1936.  Koestler's book Darkness at Noon was completed in 1940, then smuggled out of Vichy France and published the next year. Also in 1940:
A talented little group of intellectuals in the 1930s was keen on Promethean myths, and the center of that impulse was the United States, where the talented group pictured the Communist movement in the light of Prometheus and his struggles. Edmund Wilson devoted his masterwork To the Finland Station to the Promethean theme—it, too, came out in 1940, by the way.... 
By the time Wilson completed his own manuscript, he knew very well that, in Russia, Marxism had pretty much failed. And he attributed this failure largely to a philosophical error on Marx’s part, back in the nineteenth century. Marx had thoughtlessly incorporated into his own doctrine a whiff of mysticism, drawn from Hegel. The mystical whiff had transformed Marx’s movement from a sober, progressive-minded, social-science action campaign into a movement of religious inebriates. A religious frenzy had produced a hubris. Under Lenin and the Bolsheviks, hubris led to despotism. And to crime—to the deliberate setting aside of moral considerations. To the dehumanization of humanism.
Such was Wilson’s argument in To the Finland Station. Here was the Promethean myth, twisted into tragedy: a story of rebellion and counter-rebellion. Freedom and its betrayal. Fire and self-immolation. Wilson’s philosophical mentors were Max Eastman and Sidney Hook, and in that same year each of those redoubtable thinkers came out with his own variation on the same interpretation—Eastman in an essay in Reader’s Digest (which later appeared in his book Reflections on the Failure of Socialism) and Hook in a volume called Reason, Social Myths, and Democracy. In the United States in 1940, tragic Prometheanism was more than an argument. It was a school of thought.
And somehow Koestler, composing his novel under European circumstances inconceivably more difficult than anything his American colleagues would ever experience, arrived at roughly the same interpretation.
Berman goes on to discuss Alexander Berkman, a Russian-American Jewish labor organizer who was deported to Russia in 1919 along with Emma Goldman and more than 200 others. Berkman saw what was happening, fled to France, and started raising money to support persecuted revolutionaries in Leninist Russia. One of his followers was G. P. Maximoff, a Russian anarchist who was imprisoned in Moscow and then fled to Chicago. It may be surprising to hear that what Berman calls the best-documented book about terror in Russia (at least before modern times) was published with the support of the International Ladies Garment Workers Union.  
He earned his living as a wallpaper-hanger. In his free time, though, he kept up the documentary labor, and he compiled his investigations in a systematic fashion, and ultimately he came out with a 624-page volume. Maximoff called his book The Guillotine at Work: Twenty Years of Terror in Russia (Data and Documents). It came out in 1940—the year of Hemingway’s For Whom the Bell Tolls, Wilson’s To the Finland Station, Hook’s Reason, Social Myths, and Democracy, and Eastman’s essay in Reader’s Digest; the year in which Koestler completed Darkness at Noon.... [H]is extraordinary book was published by a little committee of his own allies called the Chicago Section of the Alexander Berkman Fund, who drew their own support chiefly from Berkman’s old fraternal order, the Workmen’s Circle, and from the International Ladies’ Garment Workers Union (where the anarchists were part of the power structure) and a scattering of Russian and anarchist groups in the United States.... The second half of Maximoff’s book, which contains the crucial documentation, is completely unavailable nowadays, except in a few libraries and among a very few secondhand book dealers. I would be surprised to learn that more than a handful of this magazine’s readers have ever heard of this book. Even so, of the various works from 1940 that I have been discussing, Maximoff’s The Guillotine at Work has got to be the most powerful, emotionally speaking, and the most convincing, intellectually speaking, and the most horrifying, morally speaking. The book portrays Lenin as a monster, committed to murders and terror on the hugest of scales. The book documents the portrait. The book recounts the several phases of Lenin’s policy year by year, beginning in April 1918, when the Moscow Anarchists were suppressed. The book explains the mass consequences of Lenin’s policy, beginning with a politically induced famine as early as 1921. The book recounts the gradual destruction of any sort of political freedom in the Soviet Union. The book proposes a few statistical consequences.... You also realize, reading Maximoff’s The Guillotine at Work, that here is a kind of preliminary draft of Solzhenitsyn’s The Gulag Archipelago. Did Solzhenitsyn know anything about Maximoff’s great work? Solzhenitsyn definitely knew some of the imprisoned anarchists. In his novels he describes in a somewhat sympathetic fashion the admirers of Kropotkin, living out their fate in Siberian exile. But he appears not to have known anything about Maximoff. Michael Scammell is the biographer of Solzhenitsyn as well as of Koestler, and, though his biography of Solzhenitsyn is enormous (as is the biography of Koestler), Maximoff’s name never comes up. Anyway, it is hard to imagine how Solzhenitsyn could have stumbled across Maximoff’s fat volume. Maximoff wrote in Russian, but the Chicago Section of the Alexander Berkman Fund published the book in English translation. It goes without saying that The Guillotine at Work lacks some of the rhetorical force of The Gulag Archipelago. Maximoff was a man of literary talent, even so. In reading his book, you already begin to glimpse the power that Solzhenitsyn’s work would prove to wield decades later. For here, in The Guillotine at Work in 1940, is already a total demolition, intellectually speaking, of what Alexander Berkman called, in a pamphlet of his own, “The Bolshevik Myth”—a total demolition because it blows up the Communist idea at its foundation. And what is that foundation? This is worth defining. Marx, in his own masterwork, Capital, wrote about the horrors of poverty, exploitation, famine, and class inequality. Maximoff writes about similar things. But Maximoff’s masterwork focused mostly on the horrors of incarceration. The Guillotine at Work and The Gulag Archipelago are identical in this respect. These are books about jails, not about wages. Imprisonment, not exploitation. About the Solovietski Monastery and the Moscow Taganka prison, not about factories and farms. These books offered the revelation that, under communism, the old czarist prison system, instead of withering away, had gone into bloom. And the revelation that communism’s prisons had destroyed the old Russian heroes en masse—whole movements of those heroes, not just Peter Kropotkin’s faithful readers and followers, but the Mensheviks, too, the readers of Karl Kautsky, together with the Social-Revolutionaries and everyone else. This was the news that broke communism’s back—the prison news, and not the revelation that, under communism, the proletariat had failed to thrive, even if it was true that, under communism, the proletariat had failed to thrive....
Berman, who has written a great deal about both liberal and illiberal movements, including much recently about Islamic fundamentalism, longs for the days when liberals offered a vigorous and organized intellectual response to totalitarianism:
Reading Scammell’s account, I begin to grow a little indignant about the intellectual scene in our own moment, a couple of generations after the major achievements of the Congress for Cultural Freedom. It is very odd that nothing like the Congress for Cultural Freedom exists in our time. A tremendous intellectual debate is taking place right now across huge portions of the world, with the Islamists on one side and a variety of anti-totalitarian liberals, Muslim and non-Muslim, on the other. But the kinds of liberal congresses and campaigns that Scammell describes have never taken place in our day, not on a grand scale anyway. We have human rights organizations, but we do not have sustained campaigns on behalf of the persecuted liberals in countries where organizations such as the Muslim Brotherhood wield a lot of influence. We do not even have the kinds of congresses or conferences that would allow liberal-minded writers from different countries and speaking different languages to meet each other and discuss their respective experiences and thoughts. Nor do we have any kind of sustained and coordinated effort to translate books and essays from one language to another—not on a truly large scale. On matters such as these, Hook, the old socialists of the American labor movement, Koestler, his comrade Manès Sperber in France, and their various colleagues of the 1940s were way ahead of us.