Complex sentence: In World War I, he was promoted to brigadier general, and was the commander 18th Infantry and 1st Infantry Brigade and then was appointed commander, 1st Division, A.E.F., in October 1918.
Split into simpler sentences: In World War I, he was promoted to brigadier general. He was the commander 18th Infantry and 1st Infantry Brigade and then was appointed commander, 1st Division, A.E.F., in October 1918.