But by 1920, the Indies Social-Democratic Union had renamed itself the Communist Union of the Indies, becoming the first Communist party in Asia to join the Comintern. New unions were formed on Java and Sumatra. Peasant villagers mobilized against landowners. A railway strike briefly paralyzed the plantation belt in eastern Sumatra.

It was in this context that the legendary figure of Tan Malaka first appeared. The scion of an aristocratic family from western Sumatra, Tan Malaka had spent World War I as a student in the Netherlands. He came into contact with Socialist activists and ideas, and witnessed the short-lived Troelstra Revolution of late 1918, during which Dutch social-democrats briefly tried to emulate an ongoing revolutionary uprising in Germany. In early 1919, Tan Malaka returned to Indonesia, where he was soon drawn into labor organizing. He joined the embryonic local Communist Party, quickly ascending to its leadership — before the colonial government forced him into exile, and back to the Netherlands, in early 1922.

And so it was with early experience of the revolutionary potential of combining Communism and Islam that Tan Malaka made an appearance at the Fourth Comintern Congress in Moscow and Petrograd in 1922. There, he delivered a memorable speech about the similarities between Pan-Islamism and Communism. Pan-Islamism was not religious per se, he argued, but rather “the brotherhood of all Muslim peoples, and the liberation struggle not only of the Arab but also of the Indian, the Javanese and all the oppressed Muslim peoples.”

“This brotherhood,” he added, “means the practical liberation struggle not only against Dutch but also against English, French and Italian capitalism, therefore against world capitalism as a whole.”

The official record of the proceedings notes that Tan Malaka’s impassioned plea for an alliance between Communism and Pan-Islamism was met with “lively applause.” But his memoirs recall that after three days of heated debate following his speech, he was formally prohibited from further contributing to the proceedings. The official conclusions of the Fourth Comintern Congress, including the “Theses on the Eastern Question,” are notably ambiguous on the question of Pan-Islamism and strikingly silent on Indonesia, even though the movement there was far more successful than any other Communist mobilization in the so-called East at the time.

An alliance between Communism and Islam was not to be, neither in Indonesia nor elsewhere. The strength of Communism, as a movement, was its ability to mobilize laborers to fight for better wages and working conditions through unions, whether in oil boomtown Baku or the plantations of Java and Sumatra. But as a form of government, Communism meant one-party rule, a command economy with collectivized agriculture and party-state control over all spheres of social life — including religion.