Complex sentence: After finishing his graduate degrees he joined the staff of The National Archives in Washington, DC in the Education Division before going on to teach history at Montclair Kimberley Academy in New Jersey and The Thacher School in California.
Split into simpler sentences: After finishing his graduate degrees he joined the staff of The National Archives in Washington, DC in the Education Division. He has taught history at Montclair Kimberley Academy in New Jersey and The Thacher School in California.