Complex sentence: The Khawarij opposed arbitration as a means to choose a new ruler on the grounds that "judgement belongs to God alone", and arbitration was a means for men to make decisions while the victor in a battle was determined by God.
Split into simpler sentences: The Khawarij opposed arbitration as a means to choose a new ruler on the grounds that "judgement belongs to God alone". They considered arbitration ameans for men to make decisions when the victor in a battle was really determined by God.