Complex sentence: A brother of the 1st Marquess of Hertford, and cousin of Horace Walpole, he began his military career in the War of the Austrian Succession and eventually rose to the position of Commander-in-Chief of the Forces.
Split into simpler sentences: A brother of the 1st Marquess of Hertford, and cousin of Horace Walpole, he began his military career in the War of the Austrian Succession. He eventually rose to the position of Commander-in-Chief of the Forces.