It’s also worth noting that Marvel published a massive crossover event in 2015 that was also called Secret Wars, but that was about the main Marvel universe being merged with numerous alternate universes to create a new Battleworld.
Secret Wars resulted in many big developments for the Marvel Comics universe, most notably Spider-Man bonding with the alien symbiote, which would later bond with Eddie Brock and create the super villain Venom.
Published across 12 issues from May 1984 to April 1985 (and tied into a toyline from Mattel), Secret Wars saw many of Marvel’s greatest heroes and villains being transported to the alien planet known as Battleworld by Beyonder, an ancient cosmic entity.
Stocking Battleworld with alien weapons and technology, The Beyonder wanted these heroes and villains to duke it out, but ultimately the members of both factions were transported back to Earth at the end of the event.