The zeitgeist is the school of thought that typifies and influences the culture of a particular period in time.
For the 1940’s, the desire to support the troops, save lives, and see the war to a quick and safe end was the motivation of everything. Fashion was no exception. It changed how long people wore their clothing, and it became fashionable to make things over several times over. It turned military and other uniforms into poli-chic.
The war brought changes to fashion through requiring women in the work place. It brought changes in fashion by demanding that people seek shelter at odd hours of the night. it brouht changes in fashion as nylon and chemicals to make makeup ran short.
Huge fashion changes, all pretty simply traced back to World War II.