Before men started wearing the crotch-covering legging we call trousers, everybody wore skirts in one form or fashion (see also: loincloths, tunics, togas, kilts, etc.). And why not? Skirts are far simpler to construct and facilitate more cooling air flow to the nether regions, which would've been a godsend in the pre-air conditioning days. But then, thanks to the rise of horseback infantries, trousers (see also: breeches, codpieces, tights, etc.) became the below-the-belt manly uniform of the masculine masses.
Western women, meanwhile, continued wearing skirts, and not just simple wrap-around numbers. We're talking multi-layered, heavy, floor-length ensembles often further supported and puffed out with the assistance of cage crinoline, petticoats, bustles, or other clunky foundation garments, depending on the era (see also: corsets).
In the 19th century, recognizing not only the discomfort but also the health and safety hazards of wearing the weighty skirts that swept up street trash, impeded walking (especially down stairs) and posed fire hazards, and fueled by the freer-thinking spirit of the Enlightenment, some liberal folk began calling for more "rational dress." In 1851, Amelia Bloomer debuted her signature shocking ensemble of loose-fitting ankle-length trousers -- essentially bifurcated petticoats -- underneath a shorter dress. Later in 1881, the Rational Dress Society was established in London, and it advocated women being required to wear no more than 7 pounds (3 kilograms) of underwear, which at the time would have been a major load off. But even with the popularization of the bicycle and younger women adopting bloomers as riding outfits, it would still be a long while before pants would become an all-season, any-occasion women's wardrobe staple.
Pants for ladies trickled into high fashion in earnest in 1911, courtesy of French designer Paul Poiret, who had earlier done women a solid by introducing corset-free styles. His harem pant, as seen on Downton Abbey, made the cover of Vogue in 1913. And speaking of Vogue, billowy slacks were becoming more commonplace in its pages by the 1930s, as well as on the pages of celebrity trades that showcased some Hollywood A-listers including Marlene Dietrich and Katharine Hepburn wearing them on and off screen. For the average trendy, well-heeled woman, however, pants couldn't simply be tossed on effortlessly; they came with their own set of rules (and weight requirements!) in 1939:
During World War II, though photographs show American women wearing pants in the workplace, dresses and skirts were still the go-to for properly going out in public, and Dior's post-War "New Look," swung the pendulum even farther away from the pant for a period. Really, as Worn Through underscores, it wasn't until the sexual revolution and second-wave feminism in the late 1960s and 1970s that women started wearing trousers en masse and whenever they wished -- for the most part. It wasn't until 1993, for instance, that Sen. Barbara Mikulski and Carol Moseley-Braun (the first African-American woman elected to Senate) became the first woman senators to rock pantsuits on Senate floor, forcing the Senate to lift its ban on lady trousers in the Senate. Hence, while women's adoption of pants wasn't directly fueled by militarism as it was with men, the choice to eschew a skirt was no less an epic struggle.