🚨🚨 Massive Spoilers for Dr. Strange In The Multiverse Of Madness Ahead!! You've been warned!! 🚨🚨
Dr. Strange in the Multiverse Of Madness has arrived and has left a mark on the MCU even more significant than that of No Way Home. In the film, we see Dr. Strange or 616-Strange and America Chavez on the run from Wanda, traveling through multiple universes until finally landing at Earth-838. After trying to find his alternate self, he instead comes across his friend turned foe Mordo, who captures him and presents him to The Illuminati. The introduction to the Illuminati is our first glimpse of a potential Secret Wars future as they are integral in the comics. So it would only be natural for the MCU to make its introduction finally.
After a formal introduction of all the members, we are then informed why this group feels so suspicious of 616-Strange's presence. We learn that 838-Dr. Strange had inadvertently caused the annihilation of another universe due to his use of the Darkhold trying to defeat Thanos. Reed Richards states to Strange, "The larger the footprint you leave behind, the greater the risk of an incursion." After Strange asks what an incursion is, Reed, replies, "An incursion occurs when the boundary of two universes erodes, and they collide, destroying one or both entirely." This explanation is very similar to what is explained in the Secret Wars storyline which further shows why we might be heading in that direction with the MCU as well.
With Wanda leaving the most significant footprint imaginable by wiping out the Illuminati and causing so much destruction in 838, this film could be the catalyst for the MCU's version of Secret Wars. In the comics, Black Panther is forced to reunite the Illuminati after witnessing an alternate Earth in the atmosphere. After the group investigates, they learn that a domino effect occurred after the destruction of an alternate universe. Multiple universes started being destroyed one after the other and what T'challa had witnessed was the beginning of their universe about to be destroyed as well.
This New Avengers storyline ultimately ends with the Illuminati unsuccessfully trying to use the Infinity Gauntlet, making the ultimate decision to destroy the alternate Earth, and having the likes of Dr. Doom, Dr. Strange, and Molecule Man being the only ones to "save" the multiverse from being completely destroyed. Molecule Man being the key in all of it, as he is exactly the same in every universe and was created by The Beyonders to be the bomb in each universe in case they felt that universe was flawed and wanted to destroy it.
I say "saved" because Doom is actually the reason for the initial incursion as he used Molecule Man as a weapon to kill The Beyonders and gain their power. The aftermath of that event is when Secret Wars starts and we're introduced to Battleworld. This Battleworld is essentially the remnants of separate universes put together, where multiple versions of characters rule over certain lands, though God King Doom is the ultimate ruler of it all and Dr. Strange is his right hand.
The Beyonder was first introduced in the original Secret Wars storyline from the '80s, which had him bring the Marvel heroes and villains to Battleword to fight for a wish. It was the first time in Marvel Comic's history that there was a crossover of all their properties in such a HUGE manner. The Beyonder would return for Secret Wars 2 in the '80s as well, but the existence of his species and their connection to the multiverse was further explored in Marvel's third Secret Wars in 2015.
It's also worth noting that Peter Parker is introduced to his symbiote suit in the original Secret Wars, and we did just see Venom leave behind a piece of himself in No Way Home...