Complex sentence: Niels was made king in 1104, but he was described as a passive monarch who lacked the capacity to rule and who left the affairs of the state to his queen, and with his blessing, Margaret became the de facto Queen regnant of Denmark.
Split into simpler sentences: Niels was made king in 1104, but he was described as a passive monarch who lacked the capacity to rule and who left the affairs of the state to his queen. With his blessing, Margaret became the de facto Queen regnant of Denmark.