Since the Middle Ages, the Christian understanding of slavery has been subjected to significant internal conflict and has endured dramatic change. Nearly all Christian leaders before the late 17th century recognised slavery, within specific biblical limitations, as consistent with Christian theology. The key verse used to justify slavery was Genesis 9:25-27: "Cursed be Canaan! The lowest of slaves will he be to his brothers. He also said, 'Blessed be the Lord, the God of Shem! May Canaan be the slave of Shem." which was interpreted to mean that Africans were the descendants of Ham, cursed with "the mark of Ham" to be servants to the descendants of Japheth (Europeans) and Shem (Asians). In 1452, Pope Nicholas V instituted the hereditary slavery of captured Muslims and pagans, regarding all non-Christians as "enemies of Christ."