Populists in Europe and North America like to claim that Christianity in the modern world is on the retreat against a resurgent and confident Islam. Even observers who do not subscribe to the idea that a “clash of civilizations” is occurring often conclude that Christianity is on the decline.
At first blush, the facts at the world level might seem to support this view. Between 1950 and 2015, according to census figures gathered by the World Religion Database, a large comparative project based at Boston University, the share of the world’s population that is Muslim rose from 13.6% to 24%. Over the same period, the share that is Christian fell from 35% to 33%.

But this is no open-and-shut case. The same trends look very different when broken down by region. Christianity has grown slowly since 1950 because in that year it was concentrated in two types of regions: those, like Europe, that were populous but growing slowly, and those, like Sub-Saharan Africa, that were fast-growing but still small. Islam has grown quickly since 1950 because it was concentrated in populous regions that were destined to grow fast over the next 65 years, particularly in Asia (contrary to a widespread stereotype, roughly 80% of the world’s Muslims are not Arabs). Christians made up less than 3% of Asia’s population in 1950. So, although this share had risen to 9% by 2015, too many of the world’s babies born in the intervening period were never going to be Christian anyway.
The answer is a large number of different religions that the World Religion Database classifies as “Ethnoreligions.” These local and folk practices encompass everything from spiritual healing to rites of passage, fortune telling, and preparations for love, death, and war. They may recognize gods of the village, the river, the forest, and the mountain. And while they commanded the allegiance of 42.6% of Africa’s population in 1950, this share had dropped to a mere 8.6% by 2015.

Africa is not alone. Asia has also experienced a sharp fall in the share of the population professing adherence to local and folk religions, notably those that commanded the allegiance of many Chinese in spite of efforts by centralizers from Confucius to Mao Zedong. In Latin America, where the Roman Catholic Church made inroads much earlier, most ethnoreligions disappeared in the nineteenth century.

In short, the big religion story in the last century is not one of ideological struggle between Christianity and Islam, with Islam winning. It is a story of growing corporatization, with local and folk religions everywhere being gradually but inexorably replaced by churches and mosques that are affiliated with two of the world’s main religious brands. Hinduism and Buddhism, the two other main brands, have been much slower to respond, but they are starting to change, and the growing religious assertiveness of India’s ruling Bharatiya Janata Party is just a foretaste of much bigger things to come.
Historically, religions have competed in three main ways: war and conquest, demographic rivalry, and persuasion (in the marketplace of beliefs, we might say). War and conquest were overwhelmingly the most important vehicle of religious competition throughout history until the nineteenth century, and demographic competition was overwhelmingly the most important for most of the twentieth century. Despite the turbulence in the Middle East, war and conquest have declined massively in importance as a vehicle of religious competition in recent decades. And demographic competition will fade as the world’s female children gradually have fewer of their own.

On a world scale – whatever populists may say – Christianity is not struggling; it is in more vigorous shape than it has ever been. And the marketplace is where most of the religious action is going to take place in this century. As in many other marketplaces, there are large returns to scale for those who can work out how to exploit them. That is why corporate religion is here to stay – and why we should expect it to consolidate its dominance.

This phenomenon is the religious equivalent of the displacement by Walmart and Target of local grocery stores across the United States. You may regret it or welcome it, but it has proved unstoppable.
But the world is converging demographically, and fast. One of the only iron laws governing human societies is that when women are both educated and free to work for money, they choose to have fewer children, whatever their bishops and imams may say. Fertility in Muslim-majority Iran fell as fast in the 1980s and 1990s as it had done in Communist China under the one-child policy a decade earlier. In the twenty-first century, demography will lose almost all its earlier importance in shaping the relative growth of the world’s religions.

One way to see the importance of demography up to now is to calculate what would have been the shares of Christianity and Islam in the world’s population in 2015 had the number of each religion’s adherents simply grown at the average rate of the population in their own country since 1950. Islam would have had a share of 20.2%, so its share of 24% is indeed a lot higher than expected. But Christianity would have had only 27.7%, so its actual share of 33% is also much higher than expected.

To understand what has been going on, consider Africa. In 1950, Muslims represented 36% of Africa’s population, a share that had risen by 2015 to 41.8%. Christians represented a mere 21% of the population in 1950, but by 2015 this had risen to an astonishing 48.5%. Much of this reflected the massive expansion of evangelical and pentecostalist churches across the continent, from Abidjan to Zanzibar. So, if Islam and Christianity were both getting a bigger share of the pie, who was losing out?

Posted on Project Syndicate