|Marvel's Secret Wars! Nuff' said|
Well, back in the '80s such title-spanning crossovers weren't the norm. Sure, Superman and Batman were oftentimes partnering up, and there was the Justice League, while Marvel had The Avengers and Marvel Team-Up -- but how often (prior to the mid-'80s) did heroes from nearly every popular title join forces for colossal crossovers that spanned issues and months? Hardly ever.
That all changed in 1984 -- with the advent of Marvel Super Heroes: Secret Wars, a defining chapter in comic book history.