On May 28th, 1923, the US Attorney General declared that it was legal for women to wear trousers anywhere. This was by no means the end of the matter, though it was a significant landmark. The prohibition of trousers for women was enforced in most European countries and US states not only by social custom, but by laws that punished transgressors.
Several women defied this ban, not only for freedom of movement, but for disguise, especially for runaway slave women, and in some cases to earn much more than women could earn. Several prominent women activists were arrested and sentenced for wearing clothing that was deemed appropriate only for men. Amelia Bloomer popularized the loose-fitting garment that bears her name, and bloomers caught on as women took up cycling, tennis and horse-riding. Demure ladies might ride horseback side-saddle in skirts, but most found riding-breeches more practical.
Two world wars that saw women doing men’s jobs while men were away in combat helped speed along more relaxed attitudes to modes of dress, and female pilots often preferred trousers. Many states still passed and enforced laws against cross dressing in the 20th Century, however, despite the 1923 declaration by the Attorney General. Female senators were banned from wearing trousers on the senate floor until 1993, and it was only in 2013 that a Paris by-law that required women to seek city permission before wearing trousers was revoked - it had previously allowed them only for cycling or horse-riding.
Remaining restrictions in modern developed countries are now more or less confined to institutions imposing rules, rather than legal bans. Some schools insist on a “skirts only” code for girls, and some businesses such as airlines have required them for female flight attendants. The Royal Canadian Mounted Police dropped its opposition in 2012, British Airways did so in 2016, and Virgin Atlantic began permitting trousers for its female staff earlier this year.
Some religious orders ban women from wearing men’s clothing or otherwise dressing “immodestly.” It was long banned by Christian churches, which quoted Deuteronomy 22:5 saying, “The woman shall not wear that which pertaineth unto a man, neither shall a man put on a woman's garment: for all that do so are abomination unto the Lord thy God.” And by coincidence it was on May 28th, 1431, that Joan of Arc was charged with “relapsing into heresy” by donning male clothing (i.e. military attire) again. She was convicted and burned at the stake.
Trousers on women have been symbolic of the slow transition from ancient to modern, from patriarchy to a more gender-equal society. The march into liberty took longer for women than it did for men, but the changes in social attitudes that permitted greater choice about deportment and lifestyle have been a liberating influence for both.