Last summer bore witness to the release of one of biggest superhero team up films of all time; it hit the cinemas to near universal critical acclaim and grossing 1.511.8 billion dollars worldwide (http://boxofficemojo.com/alltime/world/) that film was Avengers Assemble. Such a success story however did not occur over night, in fact the series of films that Marvel produced preceding the Avengers set the stage for its inception.
In 2008 Marvel studios released Iron Man with the actor Robert Downey Jr spearheading what we now know today as Phase 1, the film was very successful at the Box office grossing $318 million domestically and $267 million internationally but it also hooked audiences everywhere with a stinger (an after credits sequence) in which Samuel L Jackson as Nick Fury mentions the Avengers Initiative. In an act of incredible foresight Marvel studios was planning to create a shared universe in which all their characters existed in order to make this superhero team up a reality. Following Iron man and its sequel Iron man 2 other heroes soon made it the big screen, such as The Incredible Hulk (came out before Iron man 2), Thor, and Captain America; each introducing audiences to the core members of Earth’s Mightiest Heroes. (http://www.studiosystemnews.com/behind-the-money-of-marvels-mighty-movies/)
However the preceding films did more than just introduce the heroes themselves they also introduced the various elements that tied all the events in the Avengers nicely together.
The Iron man films introduced Nick Fury and the organisation called SHIELD which brought all the heroes together.
Thor introduced the film’s main antagonist Loki.
Captain America gave us the Tesseract, the film’s major plot macguffin (plot device).
In a sense the Avengers was the ultimate payoff for all of these plot threads, it was structured very much like an epic comic book crossover with several lead in stories.