Complex sentence: In addition to the chief of the army, he was also the head of the Church, but his throne was not hereditary, but elective for acclamation of the senate, army and people who, if betrayed, had the legal right to rebel.
Split into simpler sentences: In addition to the chief of the army, he was also the head of the Church, but his throne was not hereditary. It was elective through the acclamation of the senate, the army and the people who, if betrayed, had the legal right to rebel.