On April 14, 2008, Hollywood's gravitational pull got turned up a notch. That day, audiences for Iron Man were getting their first taste of the Marvel post-credits scene: "You think you're the only superhero in the world? Mr Stark, you've become part of a bigger universe. You just don't know it yet." Samuel L Jackson was nominally addressing Robert Downey Jr's billionaire playboy character Tony Stark, but really he was talking to us.
This was a pitch for a new form of franchise: the interlinking lattice of blockbusters, with superheroes strolling in and out of each other's films before tag-teaming in 2012's insanely lucrative The Avengers, that become known as the Marvel Cinematic Universe.
The semioticians once called these kind of clubby references "intertextuality". But where they appeared in cinema before, it wasn't as part of a business strategy. Quentin Tarantino, for example, likes to draw playful lines through his oeuvre: ear-slicing Vic Vega in Reservoir Dogs is, wouldn't you know it, the brother of John Travolta's Pulp Fiction hitman Vincent.
Tarantino, though, never had total world domination in mind.
Post-Marvel, an "extended universe" of connected films, has become the primary tactic of Hollywood studios for digging in their franchises worldwide.
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Batman v Superman: Dawn of Justice - out this week and setting DC Comics' square-jawed finest in a synergistic spat, as well as cameoing Gal Gadot's Wonder Woman ahead of next year's film - marks the start of the DC Extended Universe. Suicide Squad, teaming up DC's supervillains and due out in August, will be the next instalment.
There's a lot more coming down that pipe: Star Wars - now, like Marvel, Disney-owned - will sprout its first "anthology" spin-offs in the shape of Rogue One, about the team who stole the plans for the Death Star, and an untitled film about a young Han Solo.
Universal are to resurrect their famous stable of 1930s monsters, including Dracula, the Mummy and the Wolfman, while Warner Bros do the same thing, only super-sized, with the likes of Godzilla and King Kong. Paramount, meanwhile, have the Hasbro-shared universe on the drawing board, bringing together GI Joe, Micronauts, MASK and other half-forgotten 1980s playbox favourites.
The 21st-century franchise growth spurt, with the Harry Potter series running well past the traditional trilogy format into multiple instalments, was partly prompted by the rise of the overseas box office. With blockbusters making as much as 80 percent of their money outside America, belonging to a recognisable franchise was one way of selling them across culturally disparate territories.
A form of insurance against the colossal $150m-plus budgets needed to launch these global behemoths.
The extended universe is the logical step-up of this branding ploy: reinforcing the links between films, parading a character in one before giving them their own showcase, buddying them up (or the opposite, as in next month's Captain America: Civil War) in different configurations.
Always titillating the fan base, while keeping your movies in theatres frequently enough to snag the curious.
Marvel were fortunate enough to kick off their universe in the second half of the Noughties, when several competing franchises were approaching their end: Harry Potter, Christopher Nolan's Dark Knight trilogy, Twilight (and Pirates of the Caribbean running out of steam).
But its strategy, plugging its individual series into an overarching mega-franchise, pulled its own weight. Marvel's Phase One films, apart from the abortive Edward Norton Hulk (he was later replaced by Mark Ruffalo), did promising-to-impressive business ranging between $300m and $600m worldwide.
After bundling its superheroes together for The Avengers, all the cameos and after-credits teasers from the preceding films creating the sense of a dynamic universe in flux, every subsequent release, apart from last year's Ant-Man, took more than $600m.
Marvel was also lucky that its rise coincided with explosive Chinese box-office growth that boosted its income.
But the studio wouldn't have been able to take advantage without fastidious attention to the intricacies of its Cinematic Universe, with president Kevin Feige - a deeply immersed comic-book nerd - the architect-in-chief. "Phase Two", buttressed by this rigorous branding, has seen Marvel's films consistently bulk out both their US grosses (where takings often fall for sequels) and overperform internationally, too.
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The trust they've built in the brand, and its panache has allowed them to hit little-known properties like Guardians of the Galaxy, their fourth most successful film, straight off the bat.
Perhaps the extended universe's most revolutionary aspect is that, like any universe, no one knows how far it can stretch.
Unlike The Lord of the Rings, The Hunger Games and the linear model with a fixed end point that has dominated recent franchises, the new breed is pulling towards a potentially infinite form of storytelling.
The web of spin-offs and amalgamations - influenced by both the enormous body of comic-book lore currently nourishing superhero films and TV's episodic continuum - allows for more possibilities to prolong a franchise, and extend it in multiple directions, than old-time properties like James Bond.
Those also aimed to never say die, but in the most unambitious fashion, as a series of self-contained, unconnected stories.
The unique franchise gigantism that is emerging in cinema reflects the global field on which Hollywood must now operate.
Overseas box office is no longer a nice added extra for the studios; it's now an absolute imperative to be battled over. Ringing every drop out of your intellectual property and marshalling it into an all-enveloping network is one method, and Marvel Studios is built on it.
Others are following suit: after Disney bought Lucasfilm in 2012 and began developing The Force Awakens, much of the Star Wars marginalia previously laid down in novels, comics and video games was designated "non-canon" to clear space for the new trilogy.
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A change in the story-telling
Narrative storytelling is already showing signs of strain at having to operate under the extended universe's peculiarly demanding laws.
For all their adeptness at universe curation, Marvel began to wobble in last year's Avengers: Age of Ultron, which struggled to juggle the multiple plotlines that were presumably preparing the ground for future films.
The centre - another generic showdown with the obligatory megalomaniacal villain - didn't quite hold. If serialised TV is the model for these expanded franchises, they suffer from the same drawback: the obligation to elongate and embroider the story taking priority over a neat, emotionally coherent dramatic arc.
It's rare, for example, for characters to die in mainstream blockbusters - just in case they're needed in future instalments. Even if they do - like Han Solo in The Force Awakens - they can be reborn elsewhere in the extended universe; in a younger incarnation in the case of everyone's favourite space smuggler.
Reconciling these non-committal tendencies with precise, satisfying storytelling will be the great challenge for 21st-century Hollywood, in its effort to please everyone, everywhere. All these universes springing up means there's no shortage of practice space.
But with them spewing out with close to 40 movies over the next decade, they will need more inventive ploys than just colliding their protagonists into Top Trumps-style showdowns in order to continue current box office-expanding feats. The storytelling might aspire to be infinite, but the audience's patience won't be.
Source: Al Jazeera