Starting in 1995, every single X-Men title was taken over and transformed to reflect a new and terrifying timeline for the mutant heroes: the Age of Apocalypse. A dark and brutal alternate reality, the crossover was one of the most over the top moments in the entire franchise.
However, Age of Apocalypse was also one of the purest X-Men crossovers ever - featuring many elements that have proven to be crucial to other X-Men storylines.
WHAT WAS THE AGE OF APOCALYPSE?
Legion, the son of Charles Xavier and Gabrielle Heller, turned out to be an incredibly powerful mutant. Seeking to change the timeline and create a world where his father was less focused on preventing a war between humans and mutants (and therefore had more time to help raise him), Legion traveled to the past in an attempt to kill Magneto. A handful of X-Men went back in time to stop him but, in the battle, Xavier himself was killed. This changed the timeline and wiped all the time-travelers from existence - except for Bishop, whose ability to absorb energy allowed him to retain the time-traveling energy Legion had given off. There was an unintended consequence of the battle, as well. The conflict awoke Apocalypse a decade early, allowing him to easily conquer the world with little resistance.
Within twenty years, the world has become a far darker place. Apocalypse and his Horsemen rule over a world where the most vicious mutants thrive and humanity has been brought to the brink of extinction. However, a handful of people still fight back against Apocalypse's reign - notably the X-Men. Formed by Magneto as a way to honor his fallen friend and his dream of peaceful co-existence, the mutant heroes are among the only beings capable and willing to openly fight against Apocalypse. But when they discover Bishop wandering the wastelands that used to be the United States, the team learns of the core Marvel Universe and decides to do everything they can to help Bishop restore the original timeline as it was meant to be - even at the cost of their lives.
HOW IT'S EVERY X-MEN CROSSOVER IN ONE
Age of Apocalypse is one of the most ambitious crossovers in X-Men history. The story spread across every X-Men comic of the era, with different teams carrying out different missions. Other titles, like Factor X, focused on the villainous Cyclops having a change of heart, while comics such as X-Man introduced other corners of the universe and the inhabitants of it. There was even X-Universe, which featured the AOA versions of other Marvel mainstays like Doctor Doom, Thor, and Gwen Stacy; and Weapon X, which showcased the human resistance led by Bolivar Trask and his wife Moira. It was expansive in a way that many crossovers fail to be, literally touching every corner of the Marvel Universe and transforming it into a new dark, compelling, and oftentimes hyper-violent form.
The story is reflective of many of the biggest tropes that occur in major X-Men stories from before or after the event. The crossover introduced evil versions of established heroes and pitted them against the heroes. This is similar to stories like the "Dark Phoenix Saga," with long-time allies became deadly enemies. Like "Days of Future Past," Age of Apocalypse puts the X-Men in a no-win, post-apocalyptic world where the heroes have to die to save the world. The heroes were still plagued by in-fighting and feuding, however, reminiscent of stories like Schism where the X-Men fully fall apart. The differing missions and stories of the various X-Men teams told across multiple titles are even evocative of the current "Dawn of X" era - and a reminder of what Apocalypse could do if he wins.
But all those dark elements of the world helped underscore the horror of this reality, and make the few shining moments of humanity that occur all the more impactful. It makes moments like X-Man finding a surprising home with Forge more meaningful, or the sacrifices Colossus makes to try and save Illyana all the more tragic. The crossover even found ways to influence the Marvel Universe directly in the moment, eventually bringing characters like X-Man, Dark Beast, and Blink back over to the core Marvel Universe in some form, helping expand the world even while threatening to destroy it. While the hyperviolence and absurdly dark imagery may not have aged as well, the unique versions of classic characters and sheer volume of X-Men tropes makes this story stand out, even among other crossovers.