With the MCU, DCEU and Universal Monsters expanded franchises suggesting that Hollywood has a bit of a thing for tying movies together to make them even more lucrative, you'd think shared movie universes were a particularly new thing. But the reality is that it's been happening for years in far more subtle and creative ways.
As far back as the 80s, film-makers have added in fun nods to other movies that go beyond mere Easter Eggs and actually legitimately tie the movies into the same universe. They're often buried to give fans something to look for (and a reward to earn), and we've already looked at 11 examples previously including indie horrors related to hugely expansive comic book movies and a kids movie franchise and a violent Grindhouse B-movie series. Those were just the start, with far more examples out there if you put the time in to find the connections.
Sometimes, the connections are fairly obvious - as with Split and Unbreakable's shocking ending revelation - but occasionally the films demand a little extra digging.