During the previous period of mass incursions, intruders such as Goths, Huns, Vikings, Bulgars, and Magyars destroyed the antique order and reshaped Europe’s population. So far, the modern migration has been notable not for its absolute magnitude but for five special characteristics.

First, as is true for immigrants in general, the Muslim migrants are much younger than the recipient populations. Second, the migrants’ birth rate is appreciably (approximately three times) higher than the continent’s mean. Third, the immigrants are disproportionately concentrated in segregated neighborhoods in large cities: Rotterdam is nearly 50% Muslim; London’s Muslim population has surpassed 1 million, and Berlin has nearly 250,000 Muslims. Fourth, significant shares of these immigrants show little or no sign of second-generation assimilation into their host societies. A tragically emblematic illustration of this reality is that three of the four suicide bombers responsible for the July 7, 2005, attacks in London’s underground were British-born Pakistani Muslims. Fifth, whereas Christianity has become irrelevant to most Europeans, Islam is very relevant to millions of these immigrants.

Europe’s traditional ostracism has undoubtedly contributed to the lack of assimilation, but more important has been the active resistance by many of the Muslim immigrants—whose demands for transferring their norms to host countries range from segregated schooling and veiling of women to the recognition of sharıa law.

What would happen if this influx of largely Muslim immigrants were to increase to a level that would prevent declines in Europe’s working-age population? In many European countries, including Germany and Italy, these new Muslim immigrants and their descendants would then make up more than one-third of the total population by 2050 (United Nations 2000).