WARNING: The following contains spoilers for King in Black #2, by Donny Cates, Ryan Stegman, JP Mayer, Frank Martin, and VC's Clayton Cowles, on sale now.
As Knull, the dark god of symbiotes, approached the Earth, it quickly became clear that this was a potential extinction-level event for the Marvel Universe, with heroes setting aside their differences to band together and mount a desperate defense against the coming symbiote army. One of the most prominent familiar faces among the defenders were the X-Men, who recently founded their own mutant nation-state Krakoa and carried out a relatively isolationist policy as they established their own island utopia separate from humanity's prejudices and governmental meddling.
But just as quickly as the Children of the Atom extended their aid to help Earth's Mightiest Heroes protect the planet, Knull's opening salvo has already ruptured this fragile alliance before it could truly flourish in King in Black #2.
X-Men heavy hitters, including Cyclops and Storm, were among the heroes that rallied behind Captain America in the heart of Manhattan as part of a special detachment from Krakoa. However, true to his reputation, Knull easily endured the orbital defenses set up to slow him down and engulfed the planet with symbiote monsters as he descended on New York City. Despite putting up a valiant defense, Storm and Cyclops were among those absorbed by the symbiotes, rising as faithful recruits in Knull's army as the evil god scoured the city for Dylan Brock for the boy's powerful mastery over symbiotes.
As the heroes that escaped the initial onslaught regroup and recover in the Baxter Building, Black Panther is seen engaged in a holographic communication with Professor X and Magneto, with the two mutant leaders still on Krakoa. Appalled that the X-Men they sent to support the Avengers have quickly been defeated and subjugated by Knull's forces. Determined not to make the same mistake twice and risk any more mutant lives, the Xavier and Magneto deny the request for additional Krakoan aid and decide to seal their borders to defend their nation-state against the symbiotes on their own terms rather than trust their livelihood in the hands of ineffectual humanity.
While mutants still played an active role beyond Krakoa's borders after its founding at the launch of last year's Dawn of X, King in Black marked the biggest overture the nation made to the outside world and its biggest alliance with the Marvel Universe's wider superhero community. While Marvel's Merry Mutants had played a prominent role earlier this year in the crossover event Empyre, their participation was largely incited by the invading Cotati attacking Vulcan on the Moon and raising an army of the undead from the ruins of the fallen mutant nation Genosha rather than preemptively playing a more proactive role working alongside the Avengers and other heroes.
Just as Krakoa began to emerge and work alongside the outside world, the heroes' failure to stop Knull from establishing a foothold on Earth and the loss of several prominent X-Men to the symbiotes have quickly shut down channels between humanity and mutants once again, at a time when the heroes need additional support the most. Distrust and mutual tension have long fueled a divide between mutants and much of the superhero community and in the face of disastrous defeat, these fissures have become all-too-visible as the full scope of King in Black puts a strain on the heroes, forcing them to seek help elsewhere as the most fragile links they've built begin to buckle.