Complex sentence: Benedict, on the other hand, refused to stand down, so he was declared a schismatic and excommunicated from the Catholic Church by the Council of Constance on 27 July 1417.
Split into simpler sentences: Benedict, on the other hand, refused to stand down. Because of this stubborness, Benedict was declared a schismatic and excommunicated from the Catholic Church by the Council of Constance on 27 July 1417.