I watched The Avengers last night. Let's put to side all the rambling, incoherent phrases of joy about how happy it made me feel. Instead, let's just point out something I'll polish in my GM kit: why they avenged in the first place.
It's a group of adventurers and do-gooders, after all. They're not all on the screen at the same time and they aren't all friends, so why work together? It's more than just the motivation for glory, it's a concrete thing. Without giving away spoilers, if CENSORED hadn't died, none of them would have come back from their in-fighting in order to take on Loki and the invading horde. It was enough to make them see beyond themselves in order to work as a team.
For my games, this is an important technique for group cohesion - assuming that it's the kind of story that needs it. The Big Threat (tm) sometimes isn't enough by itself and needs to be made personal to each of the characters so that they take action. Characters need to be personally motivated, not generally motivated. "Fame and fortune" are bad motivations. "Imprisoning the black knight for his crimes against my beloved people" is better, especially if the black knight has done horrible things which have personal significance to the player characters.
The motivation for the Avengers to work together is personal, not general, with the possible exception of Captain America, but even he was prone to in-fighting before CENSORED died. Make it personal and you'll get better response from the characters, creating better story.