I choose the year when fashion entered a modern era. For me, this is where fashion started to be known as women bestfriends, they start to wear a comfortable clothes and bring another history for fashion now.
For example, Hats.
At 1920, you can find a lot of people--both women and men wear a hat to make a luxurious looks.
Nowadays , you can find much more people wear hat which is inspired by the year when fashion start to be known.