Complex sentence: Confidence strengthened when Struensee successfully vaccinated the infant Crown Prince Frederick against smallpox, and the attraction which had arisen between the Queen and the Royal Physician amused the King, but it was initially caused by the desire of Struensee to bring together Christian VII and his wife.
Split into simpler sentences: Confidence strengthened when Struensee successfully vaccinated the infant Crown Prince Frederick against smallpox. The attraction which had arisen between the Queen and the Royal Physician amused the King, but it was initially caused by the desire of Struensee to bring together Christian VII and his wife.