Complex sentence: Created in 1684 for politician William Douglas, also 1st Marquess of Queensberry, the 2nd Duke was created 1st Duke of Dover in 1708, but this became extinct when the 3rd duke died seventy years later.
Split into simpler sentences: Created in 1684 for politician William Douglas, also 1st Marquess of Queensberry. The 2nd Duke was created 1st Duke of Dover in 1708, but this became extinct when the 3rd duke died seventy years later.