The House of M is when the mentally ill Scarlet Witch used her powers to rewrite reality into a utopia on the urging of her brother Quicksilver.
Background[]
The Avenger known as Wanda Maximoff lost control of her powers when she was reminded of a dark chapter of her life. It drove her insane and tore the Avengers apart, killing many of them including her husband, Vision. Dr. Stephen Strange was forced to shut down Wanda's mind and Captain America had to return her to her father, Magneto, when he demanded she'd come with him. He sent her to Genosha where Charles Xavier was to help Maximoff restore her sanity. However, after six months of failure, he called upon both the Avengers and the X-Men to decide what should be done. Fearing that they would decide to kill her, Wanda's twin brother Pietro tried to appeal to his father to stop them but failed. He then convinced Wanda to use her powers to create a new reality where everyone would get what they'd want. Pietro kidnapped Xavier much to the Magneto's chagrin and combined his powers with Wanda's to create the House of M.