Complex sentence: They argued that Islam, as represented by contemporary, Non-Muslim sources, was in essence a tribal rebellion against the Byzantine and Persian empires with deep roots in Judaism, and that Arabs and Jews were allies in these conquering communities.
Split into simpler sentences: They argued that Islam, as represented by contemporary, non-Muslim sources, was in essence a tribal rebellion against the Byzantine and Persian empires. They noted that it had deep roots in Judaism, and that Arabs and Jews were allies in these conquering communities.