Complex sentence: In 1939, he fled Italy before the rule of the Nazism to live in the USA, where he taught for a short time at Yale University until moving to Columbia University, where he taught until his retirement in 1973.
Split into simpler sentences: In 1939, he fled Italy before the rule of the Nazism to live in the USA. He taught for a short time at Yale University until moving to Columbia University, where he taught until his retirement in 1973.