In 1946, the U.S. intelligence community published a series of studies on the current and future dangers threatening global peace, and among these was a surprisingly detailed essay entitled, “Islam: A Threat to World Stability.” Those remarks obviously carry a special weight in light of subsequent decades. I am not the first person to discuss the report or to praise the acuity of the authors—Middle East historian Daniel Pipes was a decade ahead of me on this. Rather, I want to stress a rather different point: What is missing from this analysis is almost as significant as what is included.

The report in question, included in an intelligence review, was produced for the Military Intelligence Division of the U.S. War Department. Noting the vast scale of the Islamic world, the authors sound very contemporary when they declare that:

With few exceptions, the states which it includes are marked by poverty, ignorance, and stagnation. It is full of discontent and frustration, yet alive with consciousness of its inferiority and with determination to achieve some kind of general betterment. . . . [It] has an inferiority complex, and its activities are thus as unpredictable as those of any individual so motivated.

Those grievances demanded urgent attention in light of the surging anti-imperialist movements in territories with vast Muslim populations. By the end of the 1940s, both Pakistan and Indonesia would obtain their independence, and the ongoing crisis in Palestine was stirring fierce militancy. The essay wisely observed that “permanent world stability” was impossible when so large a part of the world’s population existed “under the economic and political conditions that are imposed upon the Moslems.”

To all of which, we might respond, “Amen.” Yet rereading the essay today, the section that strikes us most forcefully concerns population and demography, neither of which attracted any special comment from the analysts. Yet among all the changes we can trace in the Muslim world since 1946, the most significant involves its raw numbers, and the Muslim share of world population. The essay describes a world with 312 million Muslims, over half of whom lived in the Indian continent and Southeast Asia. Thirty million more lived in the Middle East; 20 million in the Soviet Union. In 1946, Muslims represented 13 percent of the global total—and at that point, the vast majority were still subjects of the European empires.

Now consider the modern picture. Although exact numbers are contested, a reasonable estimate suggests a world Muslim population somewhere between 1.5 and 1.8 billion, five or six times what it was in 1946, or between 21 and 25 percent of the global total. In both absolute and relative terms, that is phenomenal growth in a short historical period. In 1946, the Dutch East Indies probably had a Muslim population of around 50 million, compared with over 200 million in today’s Indonesia. In the last days of British rule, the whole Indian subcontinent had some 95 million Muslims. Including the present day nations of Pakistan, Bangladesh, and India, the comparable figure today would be 500 million. Since 1946, the population of heavily Muslim Iran has grown fivefold, from 16 million to 81 million. But even in comparison with these numbers, Africa still offers the most astonishing story. The 1946 essay suggested a continental Muslim population of 40 million, compared with at least 500 million now.

Those statistics are all striking enough, but then we must compare those soaring Muslim numbers with the relatively stagnant figures for white Europeans. While Africa’s total population has grown fivefold since 1946, Europe’s population in the same period has merely doubled—and of course, tens of millions of those new Europeans are migrants, many of whom are Muslim. Had it not been for Christian growth in the Global South, Islam’s numbers would be utterly swamping those of Christianity.

To point this out is not to criticize the authors of the original essay, as the crucial trends were neither visible nor knowable at the time they wrote. In 1946, there was no reason to expect a near-collapse in European birth rates, and indeed the 1950’s witnessed the celebrated baby boom across the West. Only after the mid-1960’s did Europe enter its present birth dearth.

The  stark contrast in fertility rates between Global North and South should assuredly be counted among the most important trends in global affairs in modern times. That divide has widespread consequences. It drives migration patterns and urbanization; reshapes the environment; and redraws the boundary lines on the map of the world’s great faiths. But that ultimate megatrend was literally inconceivable even to the very well-informed in the mid-20th century.

That should be a humbling lesson for any would-be prophets today.