Complex sentence: White servicemen and civilians attacked and stripped youths who wore zoot suits because the outfits were considered unpatriotic and extravagant during wartime, in which rationing of fabric was required for the World War II war effort.
Split into simpler sentences: White servicemen and civilians attacked and stripped youths who wore zoot suits ostensibly because they considered the outfits to be unpatriotic during wartime, as they had a lot of fabric. Rationing of fabric was required for the World War II war effort.