Complex sentence: The son of Sir Mortimer Margesson, he grew up in Worcestershire and was educated at Harrow and Magdalene College, Cambridge, though he did not complete his degree, chosing instead to seek his fortune in the United States of America but the First World War intervened.
Split into simpler sentences: The son of Sir Mortimer Margesson, he grew up in Worcestershire and was educated at Harrow School. He did not complete his degree, choosing instead to seek his fortune in the United States of America; but the First World War intervened.