Complex sentence: Cardinal Richelieu, who wants war between France and England, plans to expose the tryst and persuades the King to demand the Queen wear the diamonds to a soirée that the Cardinal is sponsoring.
Split into simpler sentences: Cardinal Richelieu, who wants war between France and England, plans to expose the tryst. He persuades the King to demand that the Queen wear the diamonds to a soirée that the Cardinal is sponsoring.