Original: He was accused by his political enemy Cyril of Alexandria of a heresy that later bore his name, Nestorianism, because he objected to the popular practice of calling the Virgin Mary the "Mother of God" theotokos; he instead preached that "Mother of Christ" would be more fitting.
Simplified: He was blamed by his political enemy, Cyril of Alexandria of Nestorianism, for objecting to the popular practice of calling the Virgin Mary the "Mother of God" theotokos.