Complex sentence: She was a relatively long-lived figure in the Wars of the Roses; through her short-lived first marriage to the King's brother, the Duke of Bedford, she was firmly allied to the House of Lancaster.
Split into simpler sentences: She was a relatively long-lived figure in the Wars of the Roses. Through her short-lived first marriage to the Duke of Bedford, brother of King Henry V, she was firmly allied to the House of Lancaster.