Overwatch -- the game being released on May 24 -- doesn't really have an overarching story.
The Omnic Crisis left the world in a semi-chaotic state, but it was a period of history filled with hope for the future, thanks to the efforts of the Overwatch team.
Other than the Overwatch agents that were directly involved with taking down the omnic uprising and saving the world, no one knows what really started the Omnic Crisis.
The Omnic Crisis was pretty much that one explosive historical moment that served as the impetus for a lot of world-changing events on Earth in Overwatch.
The Overwatch team may have solved the world's biggest conflict to date when they came out victorious from the Omnic Crisis, but that didn't mean the organization was flawless.
The Omnic Crisis was a world-wide catastrophe for Earth.
Overwatch is a little different from Blizzard's standard fare.
Just announced at BlizzCon was the news that in addition to the already announced Overwatch graphic novel, which will explore the relationship between Soldier:76 and Reaper among other things, we're also going to get a series of one-shot short comics set in the Overwatch universe.