The Wall Street Crash of 1929 kicked off the Great Depression, from which the general public escaped through Hollywood. The movies became the new glamorous medium for fashion.
As another war seemed imminent, clothing became more functional and military-inspired with square shoulders. Techniques for mass production of uniforms carried over into the creation of ready-to-wear fashion.
Once World War II was underway, clothes became even more restrained. Cloth was severely rationed. Uniforms were commonly seen in public.