Complex sentence: This policy was soon reversed, however, by the influence of Mary's mother Mary of Guise and Cardinal Beaton, and Regent Arran rejected the English marriage offer, later successfully negotiating a marriage between the young Mary and François, Dauphin of France.
Split into simpler sentences: This policy was soon reversed, however, by the influence of Mary's mother Mary of Guise and Cardinal Beaton, and Regent Arran rejected the English marriage offer. He and Beaton then successfully negotiated a marriage between the young Mary and François, Dauphin of France.