Marvel had a mutant problem and Brian Michael Bendis had the solution: eight issues of alternate universe, Wolverine in a panic, melodramatic Maximoffs and three infamous words later, the mutant race were down to 198 members. Welcome to House of M, where Bendis and Olivier Coipel set up a whole world and then destroyed it, in a bonfire of the X-Gene which heralded the arrival of The Avengers: Marvel’s Most Marketed Characters.
The event storyline ran for eight issues, and was a direct follow-up from the Avengers Disassembled event which blew up Avengers Mansion and removed several members from the team. Some died, some went home, and one went particularly unstable and was sent off to live with the world’s least inspiring father figures, Magneto and Professor X. That would of course be Wanda Maximoff, who was left unsure what was real and what was a fiction after she had a break in reality.
Together, Brian Michael Bendis and Olivier Coipel worked together to find out what would happen if somebody slipped a single tempting idea into Wanda’s head, and the alternate-universe ‘House of M’ was created. For several months every book in Marvel’s line was sent into this new reality, with no indication as to whether they’d ever return again (spoiler though: they did). This was a world where mutants and humans lived together in relative harmony, with Magneto as a benevolent world-King of sorts.
A decade or so before a near-bankrupt Marvel had to recoup their losses by selling their most popular properties to film companies like Sony and Universal, and as part of that decision the X-Men rights went to Fox. With Marvel now solvent, House of M was designed to solve their licensing issues by reducing the X-Men and re-orientating their line so the Avengers were the primary focus for the company. And that is exactly what Marvel did – whether it was a move which worked creatively, however, has been up for debate in the years following.