Complex sentence: Litvak enlisted in the United States Army at the beginning World War II. He achieved the rank of lieutenant colonel, and joined with fellow director Frank Capra to make the "Why We Fight" war training film series, most of which also included actual newsreel footage.
Split into simpler sentences: Litvak enlisted in the United States Army at the beginning World War II, rising to the rank of lieutenant colonel. During this time period he joined with fellow director Frank Capra to make the "Why We Fight" war training film series, most of which also included actual newsreel footage.