Infinity isn't the only major event storyline raging across the Marvel Universe this fall. The X-Men franchise is about to become embroiled in a new crossover called Battle of the Atom. This crossover celebrates the 50-year history of the mutant heroes by uniting them in a conflict with their past and future incarnations.

X-Men: Battle of the Atom #1 Advance Review

The Mutant Gene Resurgent

Rival Schools

The Original X-Men

Crossovers can be a little daunting for new readers. That's why, just like we did for Infinity , we've put together a handy primer for Battle of the Atom., This guide will tell you everything you need to know about the current state of the X-Men and the four books involved in this crossover.In 2004, the mini-series House of M set the tone for the entire X-Men franchise for the next eight years. That story saw Scarlet Witch use her magic to erase the mutant gene from existence in a misguided attempt to protect the world from her, her family, and any other mutant that would abuse their abilities. Less than 200 mutants across the globe retained their powers. And everyone awoke to a new world where mutants were no longer the next step in human evolution, but merely a diminished species on the brink of extinction.Thus began a desperate bid for survival as the X-Men's many enemies swarmed in hopes of killing off the remaining mutants while they were at their weakest. Cyclops emerged as the new figurehead of the mutant race, with even Magneto rallying to his banner. But all seemed lost until a new mutant baby was finally born.Appropriately named Hope, she was seen as the key that would restore the mutant race to its former glory. And after a series of misadventures through time and a clash with the Phoenix Force in last year's Avengers vs. X-Men mini-series, Hope finally embraced her destiny and used the Phoenix to reignite the mutant gene.Since then, new mutants have been appearing all across the globe. Their species has been given a second chance, but there are many enemies who would either seek to take advantage of the renewed tensions between humans and mutants or simply wipe out mutants before they become the dominant life form on the planet. For a while, all the X-Men rallied behind Cyclops as he replaced Charles Xavier and guided the team through a dark new era. But that unity finally shattered in a storyline called Schism. In Schism, the rise of a new Hellfire Club and the return of the Sentinels caused a rift between Wolverine and Cyclops. Wolverine, haunted by his many dark deeds and lost friends and loved ones, wanted to ensure that the younger mutants under his care experienced a better and more peaceful life. The more pragmatic Cyclops believed that only by training each and every mutant for war could the survival of the mutant race be ensured.By the end, their friendship was shattered and the two men went their separate ways. Cyclops remained on the island nation of Utopia to train his soldiers, while Wolverine headed east and rebuilt the destroyed Xavier Institute into the Jean Grey School for Higher Learning. The rest of the X-Men were split down the middle as they were forced to choose a side in the philosophical standoff.The schism between the two factions of X-Men continues even after the events of Avengers vs. X-Men. During that story, Cyclops, Emma Frost, Namor, Colossus, and Magik were possessed by fragments of the Phoenix Force. They attempted to use their godlike powers to improve the world, but were quickly corrupted and turned on each other. In the end, a combined force of Avengers and X-Men confronted a power-mad Cyclops. They beat him, but not before Cyclops killed his old mentor, Professor Xavier. Now, many of Cyclops' old faction have returned to the Jean Grey School. Somewhat begrudgingly, Wolverine is now the legitimate face of the X-Men. However, despite being a fugitive from S.H.I.E.L.D., Cyclops has formed his own, secret school called the New Charles Xavier School for the Gifted. Cyclops is waging a guerrilla war of sorts as he attempts to recruit new mutants to his school before they can be claimed by Wolverine's team. And despite having become a pariah among the superhero community, many members of the general public view Cyclops as a heroic freedom fighter. Like a mutant Che Guevara, "Cyclops Was Right" T-shirts are all the rage among the youth of the Marvel Universe.But there isn't just a schism between Wolverine and Cyclops' schools.There's also plenty of tension within Cyclops' ranks as well. Emma Frost, Magik, and Magneto have remained by his side. However, all four are currently dealing with the after-effects of being exposed to the Phoenix, with their mutant powers either raging out of control or simply being broken. Emma also resents Scott for betraying her during Avengers vs. X-Men. Magneto, meanwhile, has shaved his head in tribute to his old friend and rival, Xavier. Magneto's loyalty is very much in doubt, and whether he's double agent for S.H.I.E.L.D., a triple agent for the X-Men, or merely serving his own ends is very much the question right now. As if a continued schism and a wave of new mutants weren't enough, life has grown even more complicated for our heroes thanks to the sudden appearance of the original team of X-Men (Cyclops, Jean Grey, Angel, Beast, and Iceman). The elder Beast, frustrated with Cyclops' inflammatory actions and facing a potential lethal genetic transformation, decided to travel back in time and bring the original X-Men to the present. His hope was that the sight of his younger self would shock Cyclops into submission and make him realize how far he's fallen.So far, that hasn't worked. Cyclops' guerrilla campaign continues unabated. And the five time refugees are horrified at a world much different from their own. Young Cyclops hates the man he'll become. Angel has discovered that his older self died and was resurrected with no memories of his past life. Beast has now seen how much farther his mutation has yet to progress. Iceman is perplexed by the sight of his older self dating Headmaster Pryde. As for Jean, she's dealing poorly with the knowledge of her death, her relationship with the Phoenix, and the many psychic memories she's absorbed. As a result, her full range of telepathic and telekinetic skills are manifesting earlier than they should.Despite this drama, the five X-Men have vowed to remain in the present until they complete the mission Beast laid out for them. On some level, they fear the idea of returning to the past, being mind-wiped by Professor Xavier, and losing any chance of averting this future they despise so much. The fact that young Angel has now deserted his teammates to join the New Charles Xavier School has further complicated matters.Regardless, Battle of the Atom begins as Wolverine and his comrades decide the time has come to send the young X-Men back to the past. But the conflict will quickly grow more complicated from there.

Head to Page 2 for alternate futures, Wolverine's complex life, and a complete issue checklist!