Complex sentence: Karplus was a child when his family fled from the Nazi-occupation in Austria; prior to their immigration to the United States, the family was known for being "an intellectual and successful secular Jewish family" in Vienna.
Split into simpler sentences: Karplus was a child when his family fled from the Nazi-occupation in Austria. Prior to their immigration to the United States, the family was known for being "an intellectual and successful secular Jewish family" in Vienna.