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"Unity" is an 18-issue crossover story published by Valiant Comics in the summer of 1992. It was conceived by Valiant's Editor-in-Chief, Jim Shooter, who wanted to revolutionize the crossover concept in comics.
The story was serialized in all nine of the Valiant Universe comic book titles published from August to September 1992 and set up several spin-off titles.
In 2012, several years after Valiant had ceased publishing comic books, they restarted their continuity and the name was repurposed for the superhero team Unity.
References
Petrilak, Joe (June 22, 1998). "THE Jim Shooter Interview". So that's when I came up with the "branching off of the tree event" and since then, I think a lot of people have done those. So when I was with Valiant, I said "All right, let's revolutionize this crossover thing again." And I thought, let's do it just in the regular books, so you don't have to go out and buy a special issue, it's just in the books. Maybe with one special issue at the end and an intro. So I'd been thinking about that for a long time, and contrived to weave the Valiant storylines together. I still think it was pretty damn good for somebody who was flying by the seat of his pants.