Describe the main events of the 'House of M' storyline.

'House of M' depicts a reality where Scarlet Witch, experiencing a mental breakdown, alters reality using her powers, eliminating all mutants except for herself and her family. This creates a dystopian society where humans are oppressed and mutants are treated as second-class citizens. The storyline explores themes of power, control, and the responsibility that comes with extraordinary abilities. The eventual undoing of House of M demonstrated the instability of reality warping and the importance of balance.