Short answers, pulled from the story.
The first issue of Shōjo-kai appeared in 1902, marking the birth of a dedicated magazine for girls. Before this moment, Japanese magazines aimed at teenagers existed but focused almost entirely on boys' interests.
Moto Hagio and Keiko Takemiya formed part of a collective known as the Year 24 Group during the early 1970s. Their works shifted focus toward internal psychology rather than external action and pioneered male-male romance as a formal subgenre within shōjo manga.
Kodansha launched Be Love in 1980 as the first magazine targeting adult women. This marked the beginning of josei manga, which shared traits with shōjo but featured older protagonists and more open depictions of sexuality.
In the 1950s, most shōjo manga were created by men like Leiji Matsumoto and Shōtarō Ishinomori. A small number of female artists emerged during this time including Hideko Mizuno and Miyako Maki who debuted within kashi-hon anthologies.
English translations of shōjo manga first appeared in North America during the late 1990s. Titles like Sailor Moon and Fruits Basket became best-sellers among female comic book readers who had been largely ignored by American publishers.