maenades asked: why did fashion change so much in the 20's?

Hemlines rose as a result of rationed fabric because of the Great War - they had less to use for the skirts so they became shorter. There was actually an attempt to lower hemlines again to ankle length after the war by the more stalwart, modest matrons, but the youthful fashionistas weren’t having it and the hems continued to rise! Knees became all the rage (they really did rouge them or put trinkets on their garters to show them off).

To explain the “boyish” figure that was en vouge in the ’20s, the silhouette had gradually been straightening and slimming since the early ’10s with the evolution of the corset shape until the hemline dropped in the 1920s to emphasize that even more.