Complex sentence: With a doctorate degree he continued in the psychological field as he became the Chair of Psychology at Indiana University in 1945, but three years later in 1948 he decided to return to Harvard when he was offered a job as a professor of psychology.
Split into simpler sentences: With a doctorate degree he continued in the field of psychology, in 1945 becoming the Chair of Psychology at Indiana University. Three years later in 1948 he decided to return to Harvard when he was offered a job as a professor of psychology.