Following the deaths of his children in The Ultimates 3, Magneto launches an attack on the Earth by reversing the magnetic poles and killing millions in tidal waves. The heroes unite to bring down the Brotherhood of Mutants once and for all. This series saw the death of many central Marvel characters, marking the biggest departure to date for the Ultimate universe from its counterpart.
The epilogue to this event is told in Ultimate Requiem.
Brotherhood of Mutants