Because the enslavement of 'heathens' was sanctioned by the Catholic Church whereas the enslavement of Christians was a sin, when Christianity arrived in Northern Europe, there arose an increasing demand for non-Christian slaves. With the end of the Viking Age around 1100 A.D., the thrall population became composed of fewer Christians and more Slavic and Scandinavian pagans. The Catholic Scandinavians had a
de facto monopoly on trading thralls because of the large pagan populations that remained in Scandinavia.