Complex sentence: All knights needed to have the strength and skills to fight wars in the Middle Ages; they not only had to be strong but they were also extremely disciplined and were expected to use their power to protect the weak and defenseless.
Split into simpler sentences: All knights needed to have the strength and skills to fight wars in the Middle Ages. Knights not only had to be strong but they were also extremely disciplined and were expected to use their power to protect the weak and defenseless.