By the 1930s, starlets like Katherine Hepburn and Marlene Dietrich openly wore pants for comfort and style, but this wasn't really an option for most women. It was the 1930s equivalent of Lady Gaga wearing a meat dress or something. Except crazier. Outside of a few brave souls, women continued to stay away from pants. The taboo was strong enough that nothing short of a worldwide war would change it.
Fortunately, it was the 1930s.
"What's this about Germany ...?"
World War II changed everything. When women entered the workforce, they did so in their husband's pants. Pants were once again seen as a symbol of patriotism, this time in the form of sacrificing silk dresses so the men could have parachutes. When the war was over most women went back to wearing dresses, but trousers became increasingly associated with working women and the Feminist Movement.
It wasn't until the 1970s that pants became a fully accepted choice for women. One major factor was Title IX, which prohibited educational institutions from discriminating on the basis of sex, meaning that colleges could no longer kick women out for wearing pants.
How could kids possibly concentrate with this waving around in their faces?
In the same year (1972), Helen Reddy recorded the song "I Am Woman, Hear Me Roar," which became a rallying cry for second wave feminists. Reddy became an icon and regularly stood toe-to-toe with the men in an ultra-hip pair of trousers. She was so devoted to pants that she even changed history by appearing as a woman sporting bell bottoms in 19th century Maine in Disney's Peter Dragon.
Her character was secretly a time traveler.
But despite the ridiculousness of the image, these trousers signified that Reddy's character was a tough, independent woman. The same was happening all over the world. Pants had come full circle as a power symbol that once gave men a convenient way to exaggerate the size of their dicks.
Seriously, pants should have their own holiday. Or at least some kind of monument or something.
For more unusual world-changers, check out 6 Mistranslations That Changed The World and 5 Horrible Diseases That Changed The World (For the Better).