Before I start, I'll let you know that what I'm going to be talking about a scene at the beginning of Avengers: Age of Ultron. The scene is early on in the movie, and it only lasts a couple of minutes, but if you don't want this minor scene to be spoiled, I advise you not to read forward.
Okay, still here? Good, let's start.
At the beginning of [The Avengers: Age Of Ultron](tag:293035), Tony Stark infiltrates Strucker's hold and locates Loki's scepter. Before he can get his hands on it, Wanda Maximoff, better known as Scarlet Witch, uses her reality-changing powers to alter the world around him. The giant Chitauri whale corpse suddenly comes to live and swims through the sky as the room turns into a piece of asteroid drifting through space.
As Tony looks around bewildered, he notices his friends, his fellow Avengers, all piled into a heap. Each and every one of them are either dead or dying, and Steve Rodgers utters a few last words about how Tony could have saved them before he joins the dead. Tony looks up to see not only a Chitauri whale, but a colossal squadron of Chitauri warriors by a giant portal. It is then that he snaps out of it, and proceeds to the scepter.
While this scene is often bypassed compared to the action-filled brilliance of the rest of the movie, it is by far the most important scene of the film. After viewing the death of the rest of the Avengers, Tony takes it upon himself to bring the Ultron program to fruition. Without that vision, Tony may have never even created Ultron.
Now here's when speculation comes into play. I firmly believe that we are going to see this same scene, or rather a slight variation of this scene, in a future Marvel film, either
part I or part II.
The films are likely to model the events of the Infinity Gauntlet comic series, in which Thanos (the big purple guy in Guardians of the Galaxy) uses the six Infinity Gems to wipe out half of the worlds population with the snap of his fingers. The remaining Avengers, X-Men, Guardians, and any other heroes band together in order to take him out, but they fail. One by one, Thanos slaughters them all.
The only way Thanos is defeated is when his grand-daughter Nebula takes the gauntlet from him and makes everything right. Before that, Earth's mightiest heroes were scattered about, each and everyone of them massacred.
I believe that Tony's vision is this exact moment in the future. For one thing, the vision takes place in space, as does this battle with Thanos. Secondly, Captain America's shield is broken, and as you can see from the picture above, Thanos is more than capable of shattering the Vibranium shield. Lastly, Tony sees a Chitauri army in the distance, and who sent the Chitauri to invade Earth? In extension, Thanos did.
Hopefully, if my theory is true, that means that the movie will be sticking close to the comics. Perhaps we will finally be seeing Nebula dethrone her evil grandfather (or just father, in the films case)!