Complex sentence: Starting there in 1954, he taught courses in modern history until March 18,2005, and in 196, he became Chair of the Social Science Department and then chair of the History Department until 1991.
Split into simpler sentences: Starting there in 1954, he taught courses in modern history until March 18,2005. In 1963, he became Chair of the Social Science Department and then chair of the History Department until 1991.