Complex sentence: Strayer taught at Princeton University for many decades, starting in the 1930s, and was chair of the history department (1941-1961) and president of the American Historical Association in 1971.
Split into simpler sentences: Strayer taught at Princeton University for many decades, starting in the 1930s. He was chair of the history department (1941--1961) and president of the American Historical Association in 1971.