STANFORD, Calif. — The crowds jostling below, the soldiers marching down icy boulevards, the roar of a people possessed: All this a young Ayn Rand witnessed from her family’s apartment, perched high above the madness near Nevsky Prospekt, a central thoroughfare of Petrograd, the Russian city formerly known as St. Petersburg.

These February days were the first turn of a revolutionary cycle that would end in November and split world history into before and after, pitting soldier against citizen, republican against Bolshevik, Russian against Russian. But it wasn’t until Rand became a New Yorker, some 17 years later, that she realized the revolution had cleaved not only Russian society, but also intellectual life in her adopted homeland of the United States.

We usually think of the 1950s as the decade of anti-Communism, defined by Senator Joseph McCarthy, the Hollywood blacklist and the purging of suspected Communists from unions, schools and universities. The prelude to all of that was the 1930s, when the nation’s intellectuals first grappled with the meaning and significance of Russia’s revolution. And it was in this decade that Ayn Rand came to political consciousness, reworking her opposition to Soviet Communism into a powerful defense of the individual that would inspire generations of American conservatives.

Rand is best known as the author of “The Fountainhead” and “Atlas Shrugged,” but before these came “We the Living,” the novel perhaps closest to her heart. It was certainly the novel closest to her life: The protagonist, a gifted engineering student named Kira Argounova, lived the life that might well have been Rand’s, had she stayed in the U.S.S.R. But whereas Kira died a dramatic death trying to escape over the snowy border into Latvia, Rand succeeded in emigrating in 1926 and soon made it to Hollywood, the “American movie city” she had written about as a Russian film student, which became her first home in the United States.