The world is not enough

Before we start, take a deep breath. If you haven't been paying attention up until now, here is where you need to consider the current superhero movie status quo and all it has achieved. It's a lot to take in.

Marvel has an expansive universe to draw from, but most of its recognizable heroes are Earthbound. The same holds true for its movies. Our heroes, for the most part, are humans who become superhuman in one way or another, dealing with unimaginable threats in just one corner of a vast shared cosmos. Marvel has so far been assiduously strategic in building that cosmos out, giving us looks of the worlds that lie beyond our solar system while always grounding us on our home planet.

Earth is going to start feeling much smaller

In Thor and its sequel, we saw Asgard and the Nine Realms, but Midgard (read: Earth) was the key to the action. In Avengers, we got the Chitauri and our first glimpse of Thanos, the mad Titan, but New York was the battlefield — as if to say New York City is a metropolis our neighbors in the next star system over might actively pay attention to. And in Guardians of the Galaxy, while we saw Xandar and the Nova Empire, Knowhere, the Kyln, and a whole host of new alien races and important figures, the beating heart of the film itself — its soundtrack — is Earth's classic rock.

We shouldn't at all expect Earth to stop being the focal point for the action going forward. After all, we still have hyperlocal characters like Daredevil and Iron Fist that'll soon inhabit this world via Netflix. But the fact is Earth is going to start feeling much smaller as we delve deeper not only into alien worlds and cultures, but also whole other dimensions opened up by both alien science and magic.

No two characters make that clearer right now than Scarlet Witch and Doctor Strange, both of whom will likely help fill out the Avengers roster after Age of Ultron. Scarlet Witch is able to manipulate reality itself by sheer will. She's done it in the comics, and while we can only guess at the extent of her powers in the films, it can be assumed that her power won't see the same limits as, say, Captain America's. Doctor Strange, a master of mysticism and the dark arts, is far from the most recognizable character in Marvel's stable, but he's also one of the single most powerful human beings on Earth, able to walk in whole other planes of existence. He's called the Sorcerer Supreme for a reason.

Their introduction only hints at what's coming ahead. Make no mistake: Ultron will present the greatest existential threat the Avengers will have faced to date, but there are far greater powers out there, even if the citizens of Earth don't have a clue what they look like. Before long, places that were once remote and walled off will be put on a collision course, and the impact will be Earth-shattering.