Hmm. Can any long-arc extended universe type stuff be traced to the 1920s? Especially in genre fiction?
Considering a hypothesis that it was a slump decade for EUs.
ee doc smith, science fiction - Skylark was published in the 20s and the 4 novel Lensman series in the same universe was published in the 30s.
also, ERB's John Carter of Mars series was serialized in the 1910s, but novelized in 1919 w/ 8 more in the 20's and 30's
Exactly...and biggest EU of all...Sherlock Holmes, almost impossible to overstate influence. Plus Oz/Baum. Holmes a major influence/template on Bertie Wooster and Jeeves, only inverted, standard pulp tactic. Current genre must EU, look to YA fiction to see future.
Yes, and you had the plays, tableaus, a movie or two, and a host of now-forgotten imitators--big platforms run a long time (cf. Tolkien). See also https://pulpmags.org/contexts/essays/pulps-and-big-slicks.html…. Some question how popular SF was in the 1920s compared to now-forgotten genres (adventure, love) + detective