Actually Nestorius determined there were two natures, not persons...
The doctrine was about Him, not her. By clarifying that Mary carried the Second Person of the Trinity in her womb, it said that Christ cannot be divided into 2 persons, but is one person only.
That's not really accurate...The definition was finished up at Chalcedon and it was determined that Jesus had two natures, human and divine which were inseparable...
Nestorius believed that those two natures were separable and therefore Mary was not the mother of the divine nature...
Your religion has made the doctrine ALL about Mary since that dicision allows your religion (in its mind) to call Mary the mother of God...The Catholic glory goes to Mary...No honest person can deny that...It's ALL about Mary...
***Nestorius believed that those two natures were separable and therefore Mary was not the mother of the divine nature...***
This is why the Church declared that Nestorius was wrong and therefore a heretic.