Part of what has helped keep Marvel Comics' Earth-616 connected, even with its many moving parts, has been through major events. More often than not, each event is about a singular enemy threatening the whole of existence, like Thanos. As a result, heroes are brought together to face the foe at the risk of heavy losses. That said, other events aren't as clearly defined, and rather than lose some heroes, entire empires could fall.
"Avengers: Disassembled" (by Brian Michael Bendis and David Finch) explored the darkest day in Avengers history as everything the team stood for was destroyed. But the true impact came when they learned that the entire situation was caused by one of their own, Wanda Maximoff. While her actions were the result of a larger internal issue for the character, the true catalyst came from Agatha Harkness, who performed an unspeakable act.
Agatha Harkness Contributed To Wanda's Breakdown?
In Avengers West Coast #52 (by John Byrne), Wanda was forced to be separated from the children she had created through magic in means that were nothing short of traumatic. It was revealed that her children, Billy and Tommy, were actually fragments of Mephisto and not entirely human. As a result, they became highly sought after as they were needed to fully complete Mephisto. In the end, Agatha Harkness was the only one that could've helped the children, but instead, she chose another direction.
Rather than aid Wanda in saving her children, Agatha saw the stakes and realized that while it was inherently wrong, the only thing she could do was let the children go and wipe Wanda's memory. From that point forward, Wanda had no recollection of the events until a passing conversation with The Wasp triggered a chain reaction that caused her to remember everything. But rather than handle the situation with tact, she unleashed decimation on The Avengers. But it was only the start of a larger decimation that would change the Marvel Universe for some time.
Agatha Harkness' Actions Led to the Avengers' Worst Tragedy
In Avengers: Disassembled, Wanda's mental breakdown at the realization of Agatha's actions and her friend's inaction caused her chaos magic to lead an all-out assault on Avengers Mansion. This included creating a version of the hero, Jack Of Hearts, to act as a bomb, killing Scott Lang. Then She-Hulk lost control, ripping The Vision in half as a Kree and Skrull invasion destroyed the mansion and caused Hawkeye to sacrifice himself. Ultimately, it took Doctor Strange to recognize Wanda as the culprit and formulate a plan to stop her.
However, even after Magneto took her, he used this as a chance to reformat the world into one better for all Mutants, leading to the House of M event. But when she realized what had been done, Wanda made the iconic command of "No More Mutants," nearly ending the entire species. So, in the end, the events of Avengers: Disassembled weren't the team's choice but Agatha Harkness's choice. While she and Wanda had a discussion in the future about her actions, it's clear that Agatha had no regrets for what she had done and was prepared for any consequences that came of it, no matter who was lost along the way.