Complex sentence: He served as the minister of McKendree Methodist Church from 1866 to 1870, during which time he authored "A Reply to Ariel", an essay about the ethnology of blacks.
Split into simpler sentences: He served as the minister of McKendree Methodist Church from 1866 to 1870. In the late 1860s, Young was the author of "A Reply to Ariel", an essay about the ethnology of blacks.