It has been around even longer then that. MGM's Thin Man six movie series ran from 1934 to 1947 and Universal made the four Mummy pictures from The Mummy's Hand (1940) to The Mummy's Curse (1944) with each a sequels to the previous. One of the most blatant sequels is Dracula's Daughter (1936) which literally picks up where 1931 Dracula left off.FPLOON said:But, I thought this has been going on even before the 21st Century... Granted, I'm thinking about the original Planet of the Apes movie series, the original Godzilla movie series (kinda), and that one french six-movie ensemble series centered around a dude choosing between two women as the overarching concept, alone, but I don't think this whole "Broken Movie" strategy has only been going on since this turn of the century... It has only gotten worrisome because now every suppose "stand-alone" movie has to leave a [more prominent] reference or two to either remind viewers that this is part of a similar timeline/universe as the other movies that came before or will come after this one or, worse, you can tell that the movie cannot be viewed without watching the movie that came before or after it, even if there isn't anything that connects them together outside of the character roaster, maybe...
It is not well known but the first major film, Birth of a Nation (1915) had a sequel: The Fall of a Nation (1916).