Pastor Jeff Meyers writes to correct my quotation of Kuyper on Christian conversions to Islam, and points me to Rodney Stark’s The Triumph of Christianity: How the Jesus Movement Became the World’s Largest Religion 
This false belief arises partly from “the failure to distinguish ‘conversions by treaty’ from changes in individual beliefs and practices.” Some tribes signed treaties and fought with Muhammad, but “these pacts had no individual religious implications.” Berbers, for instance “converted” on treaty paper, and that permitted them to share in wars of conquest, but “the actual conversion of the Berbers in terms of individual beliefs was a slow process that took many centuries.”
Stark also suggests that some “conversions” had more to do with compulsion and opportunism than a real change of belief: “in 1292 the Coptic Christian scribes serving the Mamluk sultan in Cairo were given the option of conversion or death. Not too surprisingly, they chose to convert although even the sultan knew their conversions ‘were not taken very seriously.’”
In a charge (206), Stark draws from Richard Bullet’s research to show that it took more than two centuries for half of the population to convert in Syria, Iran, North Africa, and Spain.
