Whether you like his films or hate them, M. Night Shyamalan pulled off an impressive ruse with the release of Split, as it was a film seemingly independent from any of his previous endeavors, only for the film's final moments to confirm that the narrative took place in the same universe as his 2000 film Unbreakable. Now that Glass is in theaters, we know exactly how the events of those two films tie together in ways far more fascinating than just a cameo from Bruce Willis.
WARNING: Spoilers below for Glass
In Unbreakable, David Dunn (Willis) was the sole survivor of a train derailment, which led to his character's discovery that he was nearly invulnerable and also possessed super strength. He made this discovery with the help of Elijah Price (Samuel L. Jackson), a man whose incredibly brittle bones encouraged him to find someone out there who was his opposite.
In Split, Kevin Crumb (James McAvoy) suffers from a dissociative identity disorder, leading him to kidnap young girls as a sacrifice to one of his supernaturally powerful identities, The Beast. Crumb evaded capture in that film, with its final moments showing the Dunn would begin his quest to find the character.
Looking back, Split felt far more like a spinoff of Unbreakable than a sequel, yet key revelations in Glass have confirmed how it all ties together.
One of the formative experiences in Crumb's life was the death of his father, as his abusive mother damaged his own personal identity, which is what led to his other identities taking control over his mind and pushing Crumb to the far corners of his psyche. Without his father around, he had no one to protect him, with his death sparking the dangerous trajectory.
David Dunn's son Joseph (Spencer Treat Clark) investigates Crumb's father and discovers that he died on the train derailment that David survived. For those of you who don't remember the events of Unbreakable, the final moments revealed that Price had been the one responsible for not only this train derailment, but many other major disasters that killed hundreds, all while searching for someone who couldn't be hurt. This means that Price was ultimately responsible for inspiring Crumb's descent down a dark path, yet this was merely an unintentional repercussion of his actions.
While this detail does help develop a stronger connection between all three films, the narrative of Glass never necessitated such a connection, as it's a reveal that happens late in the adventure and doesn't have a drastic impact on the story. Regardless, fans who were expecting to see more narrative threads tie the events of the three films together will likely appreciate this connection.