How can this be? If Christian numbers are exploding, how can they be left so far behind Muslims in the rate of expansion? The answer lies in differential demographics, namely that some parts of the world are growing much faster than others. Islam grew so mightily because Muslims were so heavily concentrated in those regions that maintained very high fertility rates throughout the twentieth century, chiefly in Africa and Asia. A rising tide lifts all faiths.

In contrast, overall Christian numbers lagged because that faith was traditionally concentrated in Europe, and Europe’s demographic growth has been very slow in comparison with other parts of the globe. Back in 1900, Europeans made up around a quarter of the world’s population, but by 2050, that number will probably be closer to eight percent. In 1900, there were three Europeans for every African. By 2050, there should be three Africans for every European. If we take Europe out of the picture, then, Islam and Christianity have been running a very close race worldwide, but Christians find it hard to overcome that demographic handicap.

When I am asked about the world’s fastest growing religion, then, I answer unequivocally: Islam. Or, Christianity outside Europe.