All info and quotations from Katie Hickman's Courtesans.
After the French Revolution, fashion did away with the old method of dressing, which had been to cover your body with a bird cage, throw 3,000 feet of fabric and a garden on top of it, and call it pretty:
People were sick of the fussiness and discomfort of being hooked and strapped and padded within an inch of their lives, and made bigger and clumsier until they couldn't fit through doorways anymore. This style represented the old, decadent way of living and it still is, since we tend to correlate this style almost exclusively with Marie Antoinette.
So now that France was starting a new century out from under the yoke of monarchical oppression, styles turned back to the literal sense of the word "republican" and people started dressing like ancient Greeks.
Everything became simple, loose and flowy, they wore very few undergarments, hemlines got higher–in short, people in France felt liberated and fashioned reflected that. It migrated to England almost immediately, and this style is now synonymous with the English Regency period and Jane Austen, but its origins are very much French. Like most major fashion movements. Let's not kid ourselves.
Okay, enough with the history lesson. Here's the fun bit: Courtesans, as usual were always at the top of the fashion pyramid. They were the first ones to respond to or start trends (if you told me today that a courtesan was responsible for jeggings, I'd believe you). And, since they were sexual beings, this new revealing style of dress was basically free advertising. They took advantage of it.
"The first attempts at this style of dress were radical in the extreme. The single, chilly, chemise-like garments were so flimsy that they exposed the breasts almost entirely, while clinging to the rest of the body in a most indecent way–an effect which could be artfully exaggerated by the more daring, who would dampen the muslin of their dresses to make them cling still more revealingly" (161).
Which was all well and good, until the harsh winter of 1799, which turned Europe into one giant Fortress of Solitude. So people were like, "Okay, it's been really fun being mostly naked, but I think this is the world's way of telling us to compromise and maybe put on some goddamn underwear. Oh, wait, we have to invent it first."
Underwear became the new big thing, and courtesans were very likely the ones who led the way on this. Not everyone liked underwear, however, because they were ugly and inconvenient. And crotchless. Which in my opinion, kind of defeats the purpose. "Originally, drawers consisted of two separate 'legs' tied together at the top with tape" (163), like so:
These are TOTALLY POINTLESS, and prone to coming untied, as one woman noted: ''They are the ugliest things I ever saw . . . I will never put them on again. I lost one leg and did not deem it proper to pick it up again and so walked off leaving it in the street'" (163). Keep in mind that I'm totally a Never Nude, so just looking at these assless chaps makes me uncomfortable.
People eventually got their crap together and invented Underwear 2.0, which was shorter (so it wouldn't show under your flimsy Grecian dress) and prettier, and kept your bum warm, and wouldn't fall off in the middle of a dinner party.
And then the courtesans, as usual, started adding ruffles and lace and pretty things to entrance the menfolk, and then respectable women got in on it, and bloomers/pantaloons/drawers got really popular and eventually descended into the underwear you are (probably) wearing right now.
And that's how dead aristocrats, winter and a bunch of hookers combined their powers to invent undapants. The end.