My question is prompted by this article on SmithsonianMag.com, which discusses the book Sex and Unisex: Fashion, Feminism, and the Sexual Revolution by Jo B. Paoletti. As a warning, the cover image of that book is slightly NSFW, but here's a link to it if you're interested.
To quote the article:
Between 1965 and 1975, gender bending infiltrated American life as part of a movement called "unisex."...
Fashion is what got it there. The New York Times first used the word “unisex” in a 1968 story about chunky “Monster” shoes, and it came up five more times before the year was over. Department stores and catalogs created new sections of his’n’her clothing, advertised by couples in matching lace bell-bottoms and burnt-orange button downs.
I'm not questioning this article's main point or that of the book (though if anyone wants to discuss that it would certainly be interesting), but this did make me wonder if this was the first time that clothing designed specifically to be unisex was a major fashion trend. I assume clothes have been similar for different genders at various times in history, but was this unisex movement of the 60s-70s the first time that clothes were intentionally designed to be mostly the same across genders?
You may be interested in the answers to this question: Older history of gender, unisex clothing, effeminacy etcetera, which address some unisex or borderline-unisex clothing in the Middle Ages.
This is technically a "throughout history/the world" question and so very hard to answer, but in Euerope/the US and apart from the early years of the houppelande and toddler dress through the early 20th century - no. Women's and men's dress (within these time/place constraints, and outside of male/female stage impersonators) have had a relationship in which they influenced each other and have used elements of broader art movements in similar ways, but there was not a period in which men and women could wear the same clothing in different sizes. I can go more into both the back-and-forth influence and/or the reflection of artistic movements if you want, but the actual unisex trend Paoletti discusses is not older than the 1960s-1970s.