Complex sentence: Because of the strength of the Communist Party of China and the importance of the Marxist interpretation of history in legitimizing its rule, it was for many years difficult for historians within the PRC to actively argue in favor of non-Marxist and anti-Marxist interpretations of history.
Split into simpler sentences: Because of the strength of the Communist Party of China and the importance of the Marxist interpretation of history in legitimizing its rule. It was for many years difficult for historians within the PRC to actively argue in favor of non-Marxist and anti-Marxist interpretations of history.