Complex sentence: This was a decision with long-lasting repercussions in Islamic history: not only did the military acquire a predominant position, but it also increasingly became the preserve of minority groups from the peoples living on the margins of the Islamic world.
Split into simpler sentences: This was a decision with long-lasting repercussions in Islamic history. Not only did the military acquire a predominant position, but it also increasingly became the preserve of minority groups from the peoples living on the margins of the Islamic world.