Read about it in the works of the Ecumenical Patriarch, St. Photios the Great. The addition of filoque by Rome, was one of the causes of the Great Schism.
It still separates the Eastern Orthodox Christians from BOTH Rome and the Prostestants.
This is certainly true of the filioque controversy, but since it has to do with whether the Third Person of the Trinity was sent by The First Person AND the Second Person, or WITH the Second Person, it has nothing whatsoever to do with Nestorianism or Arianism, which is rejected by Orthodox, Catholics, and nearly all Protestants. It is therefore off-topic for this thread, which touches on theology only in the relationship between Nestorian Christians and other Christians.