[ He motions to the TV ] Things between omnics and and people started out... rough. Rougher than they are now.

They rebelled against their creators an' the world at large. That was the start of the Omnic Crisis. Overwatch was a specialized force created to combat the omnics. A lotta folks called 'em heroes, but eventually the Crisis ended, and Overwatch fell outa favor with... well, with everybody.

They imploded after that. Tension in the ranks, that kinda thing. Officially, they been inactive ever since.