The two things I think Tumblr really changed are, I think before Tumblr the primary language of fandom was text-based, and it was very much fic and filk—very text-oriented. I think Tumblr changed it so that the culture of memes as a form of communication and visual communication really became, not just a primary, but possibly now the primary way that fans communicate—the shorthand fans use. I think Tumblr played a large part in that, because before, platforms were based around text and there wasn’t an easy way to share—and it was before people really got comfortable with GIFs. So, changing to a visual language in fandom is a lot of what I think we can thank Tumblr for.
But I also think there was a lot of fragmentation in fandom pre-Tumblr, specifically because you had different platforms—you had LiveJournal folks, you had Yahoo! Groups folks. And especially if you were in Groups, it was super specific, and you could have a whole community just based around one particular ship and never really venture out into other places. And now Tumblr creates more of a panfandom community where there’s overlap between fandoms, there’s conversation that’s relevant to different fandoms. You can kind of have it all in the same space, while previously it was much more difficult, and it would be discouraged.
Keidra Chaney in Morimoto, Lori. 2018. “Roundtable: Tumblr and Fandom.” In “Tumblr and Fandom,“edited by Lori Morimoto and Louisa Ellen Stein, special issue, Transformative Works and Cultures, no. 27.