Complex sentence: From 1938 to 1941, Hardeen was featured in Olsen and Johnson's Broadway revue, "Hellzapoppin", and during World War II he performed for the troops (as his brother had done during World War I).
Split into simpler sentences: From 1938 to 1941, he was featured in Olsen and Johnson's Broadway revue, "Hellzapoppin". During World War II, he performed for the troops (as his brother had done during World War I).