Complex sentence: He graduated, first, from Bowdoin College in Brunswick, Maine, where he was an active member of the Beta Theta Pi Fraternity, and then from Cornell Medical School before becoming a physician for the United States Army during the Korean War.
Split into simpler sentences: He graduated, first, from Bowdoin College in Brunswick, Maine, where he was an active member of the Beta Theta Pi Fraternity, and then from Cornell Medical School. Following graduation from Cornell, he became a physician for the United States Army during the Korean War.