Complex sentence: Exchange of excommunications by his representatives and those of (Pope Leo IX)? started the Great Schism in 1054 which was finally abolished in 1965 when Pope Paul VI and Patriarch Athenagoras met in the Second Vatican Council.
Split into simpler sentences: Exchange of excommunications by his representatives and those of (Pope Leo IX)? started the Great Schism in 1054. In 1965, those excommunications were rescinded by Pope Paul VI and Patriarch Athenagoras when they met in the Second Vatican Council.