Jim Shooter has been editor in chief for several years. Marvel's readers are constantly asking for a story involving all the heroes and all the villains. Mattel is looking for some kind of event to do a toy tie-in with. Shooter's answer? Secret Wars.
Secret Wars I was a crossover that played out in 12 monthly issues debuting in mid-1984. The idea was to bring all the Marvel heroes and all the villains together for an epic battle that would have an effect on the entire Marvel universe.
Shooter asked all the big name books to leave an opening for the story during a particular month. Those characters would disappear for the Secret Wars at the end of their regular books and reappear in the next issue of their regular books with the effects of the Secret Wars in tow.
Readers of the regular series would wonder where Spider-Man's new black costume came from, how did Hulk break his leg and why did The Thing stay on the alien planet. To find the answers, they'd purchase the 12 issues of the Secret Wars.
Secret Wars was extremely profitable and at the time, everyone was raving about it. 20 years later, many people are quick to write the whole thing off as a marketing ploy. Shooter was the brains behind the story and wrote all 12 issues.
Shooter chose to write it himself obvious reasons. All of the other writers were so protective of their characters they would have a fit if someone else was to do the writing. Shooter figured everyone already hated him because he wouldn't let people hack anymore, so if people were going to get angry at someone, it might as well be him.
Shooter was right about the writers disliking him because aside from Spider-Man's black costume and The Thing staying on Battleworld, most of the writers quickly wrote the repercussions of the Secret Wars out of their stories. By the time the last issue of the Secret Wars was published a year later, only The Thing was still referencing the effects.
Secret Wars I was so financially successful, that Marvel asked for an encore. Secret Wars II was launched a mere 3 months after the 12th issue of Secret Wars I was published. The idea was to do the same thing, but different.
In Secret Wars II, the setting was Earth and the structure of the story was different. There was still a limited series titled Secret Wars II that spanned 9 issues, but this time, they used the tree- branch effect and had the Secret Wars story run into all of the regular series via special tie-ins.
Aside from reading the 9 main issues, the stroy branched into 22 other series that spanned 33 books. The 9 main issues were written by Shooter as well as Daredevil 223 which was a Secret Wars II tie-in.
Secret Wars II was completely wrapped up by the middle of 1986 but references to the Secret Wars would still surface. Thor 383 would have an untold story from SWI and the Fantastic Four would engage in an epic battle sub-titled SWIII at the end of 1988. Quasar, Deadpool Team-Up and What If would also briefly touch on the SW. Twenty years after SWI, a trade paperback reprinting SWI 1-12 was published.