Complex sentence: Clark was an Instructor at Colorado College from 1908 to 1910 and at Amherst College from 1910 until 1915, when he left to join the faculty of political economy at the University of Chicago.
Split into simpler sentences: Clark was an Instructor at Colorado College from 1908 to 1910 and at Amherst College from 1910 until 1915. In 1915 he joined the faculty of political economy at the University of Chicago.