Complex sentence: There are numerous examples of those of the same church fighting and killing each other and those from different churches collaborating and shows the upheaval within Christianity as a causal factor in reaction to the root cause of the rise of the secular state.
Split into simpler sentences: There are numerous examples of those of the same church fighting and killing each other and those from different churches collaborating. He shows the upheaval within Christianity as a causal factor in reaction to the root cause of the rise of the secular state.