Complex sentence: The council began when Emperor Constantine IV, wanting to heal the schism that separated the two sides, wrote to Pope Donus suggesting a conference on the matter, but Donus was dead by the time the letter arrived.
Split into simpler sentences: The council began when Emperor Constantine IV, desired to heal the schism that separated the two sides. He wrote to Pope Donus suggesting a conference on the matter, but Donus was dead by the time the letter arrived.