Complex sentence: Nyong'o took teaching positions at the University of Nairobi where he was a Professor of Political Science and a visiting professor in universities in Mexico and Addis Ababa where he served until 1987, before taking up the position of Head of Programs at the American Academy of Sciences.
Split into simpler sentences: Nyong'o took teaching positions at the University of Nairobi where he was a Professor of Political Science. He was also a visiting professor in universities in Mexico and Addis Ababa where he served until 1987, before taking up the position of Head of Programs at the American Academy of Sciences.