Complex sentence: He then moved to the United States where he taught from 1956 to 1968 at Fordham University in New York and then as Professor Emeritus at The University of Kansas in Lawrence, Kansas, until 1990.
Split into simpler sentences: He then moved to the United States, where he was a Professor from 1956 to 1968 at Fordham University in New York. As Professor Emeritus, he then taught at The University of Kansas in Lawrence, Kansas, until 1990.