Hitler, like virtually all socialists, was an atheist. But religion did have its uses, with some religions more useful than others.

‘It’s been our misfortune to have the wrong religion,” Hitler complained to his pet architect Albert Speer. “Why did it have to be Christianity, with its meekness and flabbiness?” Islam was a Männerreligion—a “religion of men”—and hygienic too. The “soldiers of Islam” received a warrior’s heaven, “a real earthly paradise” with “houris” and “wine flowing.” This, Hitler argued, was much more suited to the “Germanic temperament” than the “Jewish filth and priestly twaddle” of Christianity.

And how did it matter?

Muslims fought on both sides in World War II. But only Nazis and Islamists had a political-spiritual romance. Both groups hated Jews, Bolsheviks and liberal democracy. Both sought what Michel Foucault, praising the Iranian Revolution in 1979, would later call the spiritual-political “transfiguration of the world” by “combat.” The caliph, the Islamist Zaki Ali explained, was the “führer of the believers.” “Made by Jews, led by Jews—therewith Bolshevism is the natural enemy of Islam,” wrote Mahomed Sabry, a Berlin-based propagandist for the Muslim Brotherhood in “Islam, Judaism, Bolshevism,” a book that the Reich’s propaganda ministry recommended to journalists.

Moreover, the tentacles from the 1940s reach into the present and the likely future.

Haj Amin al-Husseini, the founder of Palestinian nationalism, is notorious for his efforts to persuade the Nazis to extend their genocide of the Jews to the Palestine Mandate. The Mufti met Hitler and Himmler in Berlin in 1941 and asked the Nazis to guarantee that when the Wehrmacht drove the British from Palestine, Germany would establish an Arab regime and assist in the “removal” of its Jews. Hitler replied that the Reich would not intervene in the Mufti’s kingdom, other than to pursue their shared goal: “the annihilation of Jewry living in Arab space.” The Mufti settled in Berlin, befriended Adolf Eichmann, and lobbied the governments of Romania, Hungary and Bulgaria to cancel a plan to transfer Jews to Palestine. Subsequently, some 400,000 Jews from these countries were sent to death camps. . . .

Fearing Muslim uprisings, the Allies did not try the Mufti as a war criminal; he died in Beirut in 1974, politically eclipsed by his young cousin, Mohammed Abdul Raouf al-Qudwa al-Husseini, better known as Yasser Arafat. Meanwhile, at Munich, the surviving SS volunteers, joined by refugees from the Soviet Union, formed postwar Germany’s first Islamic community, its leaders an ex-Wehrmacht imam and the erstwhile chief imam of the Eastern Muslim SS Division. In the 1950s, some of Munich’s Muslim ex-Nazis worked for the intelligence services of the U.S., tightening the “green belt against Communism.”

The most important lesson from history is how unpredictable it is. The likelihood that Christianity will be the dominant religion of Europe a century from now is already looking very unlikely and becoming less likely by the day.