In the last twenty years of their publication, the X-Men have been through a lot. It all started in Grant Morrison's seminal New X-Men run. Cassandra Nova, Professor X's twin sister that he thought he killed in the womb (New X-Men was way more awesome than words can ever express), used a wild Master Mold to create Mega Sentinels which she unleashed on the island of Genosha, killing sixteen million mutants in minutes.
A few years later, in House Of M, Scarlet Witch uttered the fateful words, "No more mutants," changing the Marvel Universe and the X-Men forever... or for just a few years until the whole thing was undone. Both of these events had huge ramifications for mutantkind, but which was worst for mutants?
10 The Genoshan Massacre: The Loss Of A Symbol
Once upon a time, Genosha was an island controlled by a government that enslaved mutants. Writer Chris Claremont used it as a metaphor for South African apartheid because Chris Claremont was all about using allegory and metaphor to teach young readers about the world.
When Magneto was ceded the island by the UN, it took a symbol of mutant oppression and transformed it into a symbol of mutant hope. The day the island's population was destroyed is the day that hope was destroyed as well.
9 House Of M: It Didn't Just Affect The 616 Marvel Universe
When Scarlet Witch uttered those fateful words, all but two hundred mutants lost their powers, completely changing the fabric of mutant and human relations. However, this change didn't just affect the 616 Marvel Universe.
In Warren Ellis's vastly underrated Astonishing X-Men run (go check it out- it's amazing), it was revealed that Scarlet Witch's depowering of mutants had spread through the multiverse.
8 The Genoshan Massacre: The Loss Of A Homeland
After Magneto took over the island nation, he kicked out all the humans (as per his deal with the UN) and opened Genosha up to mutants. He gave mutantkind a place where they could finally be free, feel secure, and gave them something that they'd never had before - a home. Even for mutants who didn't live there, just the idea of having a homeland gave them a feeling of confidence and belonging.
The day the Mega Sentinels landed, mutantkind lost their home. One they'd barely had time to get used to.
7 House Of M: The End Of Mutant Ascendancy
One of the first things readers learned in Morrison's first issue of New X-Men is that the Beast had not only identified the extinction gene in humanity but there was also a mutant population boom, heralding the beginning of mutantkind's dominance of Earth.
Mutants started to form their own culture, creating their own fashions and music, influencing the human world as happens whenever a new culture is introduced. Scarlet Witch's fateful utterance ended all of this, throwing mutantkind into the trash can.
6 The Genoshan Massacre: The Loss Of Security
A home is an important thing. It gives people a place they belong which fosters a sense of security and that feeling is important. That feeling was something that mutants had never had before. The closest they had was the Xavier Institute and that place got attacked every other month.
Genosha was a chance to have a place where mutants could finally feel secure and protected and that was shattered when the Mega Sentinels descended.
5 House Of M: A Skewed Balance Of Power
The mutant population boom gave mutants a lot more power in the world even with the loss of Genosha. The power dynamic between the governments of the world and mutantkind had been changed. On M-Day, that balance was thrown all out of whack.
The few remaining mutants flocked to the Xavier Institute and the US federal government stepped in, ringing the property with Sentinels ostensibly to "protect" mutants and confining them to their own reservation.
4 The Genoshan Massacre: An Incalculable Loss
One of the worst parts about the loss of the Genoshan mutants was that it represented a loss of so much potential, not just from the standpoint of lost power but individual potential. Sixteen million lives were ended and anything that they could have done was burned away by the Mega Sentinel's death rays.
Potential scientists, musicians, philosophers, writers, actors, sculptors, painters, fashion designers, and more were gone in a flash.
3 House Of M: The Radicalization Of Cyclops
Cyclops would take the lead of the mutant race after M-Day, leading his fellow mutants into a whole new world, one where their entire race could be wiped out as an afterthought. The stress of this began to wear away at him, causing him to make decisions he never would have in the past.
Cyclops had to sacrifice much of his morality to keep the mutant race going and a lot of his decisions led to some very bad things for both mutants and the world at large.
2 The Genoshan Massacre: The Trauma Is Forever
As bad as the depowering of mutants was, it all worked out in the end and was able to be overturned. Working together, Scarlet Witch and Hope Summers were able to use the Phoenix Force to reignite the spark of the mutant race around the world, giving mutants back their powers. Even now, with mutants again having a homeland and power in the world, there is a way to give back powers to the mutants who lost them using the resurrections protocols.
The Krakoan mutants are even working to resurrect every mutant who died on that day but that doesn't erase the giant stain on the mutant psyche it represents. That doesn't erase the knowledge of it and it's been shown that trauma passes into the new life of the resurrected. It doesn't change the hate that day represented.
1 House Of M: A New Boogeyman
As revealed in recent issues of X-Men, Scarlet Witch has become a vilified monster to mutants. They say that she was a pretender, as it had been revealed that she wasn't a mutant, that tried to destroy the mutant race for her own selfish ends.
This gives mutant children a thing to fear - that they can lose their identity, that which makes them special, to the whims of a monster that is beyond their control.