The system is at fault, and so is Eren - A systemic look into Attack on Titan and Eren’s trauma, and the solution to it all.
I think that one of the points the series makes about Eren’s character is that the rumbling and the subsequent genocide it caused was his fault, but also the world’s. Attack on Titan denounces humanity’s cruelty, but it doesn’t absolve responsibility from Eren either, and I think that’s a genius way of looking at the morality of our protagonist’s actions.
Understanding Eren’s Trauma
The driving force for Eren's character is his wish to be free because he was “born into this world”, though if you allow me to go deeper into the WHY he thinks that way, I’d argue it’s not only in his nature as many often argue; it was also boosted by the fact that he lived surrounded by walls to protect humanity from titans (and I’d say both the titans and the walls represent the antithesis of freedom to Eren) in one of the poorer districts of the city, in which everyone craved security and stability over the risks that came with venturing out, which Eren considers the behavior of cattle. Everything around Eren is telling him that he isn't free.
And of course, the defining moment that turns this desire for freedom into obsession is his mother’s death, which could have been prevented if the symbols of Eren’s lack of freedom were gone. Rather than just sources of frustration, the walls, the titans and Eren's own lack of ability become reminders of the loss and suffering inherent to being trampled by the strong—the pain that comes with not being free.
To understand his subconscious thought process more, I picture it like this:
“If humanity ventured outside the walls, exercising their freedom and killing the titans, this wouldn’t have happened.”
“If we didn’t live in Shiganshina, a dangerous district where the poor live due to being so close to the outermost wall, this wouldn’t have happened.”
And coupled with this, comes his own lack of exercising his freedom:
“If I had been strong enough to do what I wanted, this wouldn’t have happened.”
Eren's trauma is reaffirmed again and again, by failing to save Hannes, then failing to save Armin, and so on, and it all builds up to make him become who he is in the final act of the story.
Later on, it's revealed that Marley, actual humans, just like them, are the real villains behind Eren's opression. And that's when our protagonist snaps. It's no coincidence that the whole point of his genocide is to end civilization as we know it—he can't stomach a world in which everything that happened was by the hands of humans, one in which the monsters have families and insecurities just like him—it's just too nuanced, and that's too much to handle for Eren. It's easier to trample over everything and restart, than to face his inferiority complex, one that has its roots in the symbols that trample over his freedom, rather than solely on his nature.
From Personal to Systemic (and viceversa)
However, if we look even further than Marley to point towards someone to blame for these symbols, Marley became the way it is because human civilization was responsible for the divides that now can be seen not only inside, but outside the walls.
To put it in a simpler way, why did Attack on Titan start? Because King Fritz enslaved Ymir, someone with the power to become a titan. But we should go into the why, shouldn’t we? And it’s because that’s how human civilization works. The ones in power use it to their advantage and leave a wave of trauma that lasts generations, all to make up for their own weaknesses and fears. It’s about how the personal becomes systemic, and viceversa; and that’s exactly what happens with Eren. He represents the ultimate way in which you can trample over someone's freedom, which is met with retribution (and at the same time being an attempt at making up for his horrible trauma.)
I’d have to get into a whole rant about systemic issues and the feudalism that laid the basis for capitalism for this to become more understandable, but in the end, I’m saying all of this to prove a pretty simple point: it’s all about the cycle of hatred, which isn’t simply about revenge. It’s years and years of systemic oppression, combined with circumstance, combined with nature, and how all of it is processed by Eren’s self-esteem and ego, that led Eren to become who he is.
The line between the outside and the inside blurries, and black and white thinking become shallow in comparison to the nuance of the world—just like Eren's worldview.
Of course, I’m not saying that Eren realized all this. Dude was probably angry with the titans because they killed his mom and that was it. But a lot of it was probably part of his subconscious, and even if all of it wasn’t, all of these horrible circumstances were a vital factor in what is what the Marleyan general calls out for what it is:
Except this time, it’s not just by the Marleyan's hands. Nor is it even present humanity's.
It’s everything.
Eren is to Blame
All of what I showcased explains Eren’s insecurities, trauma and subsequent decisions. It’s because of his nature, coupled with the terrible circumstances he was born into, that shaped him into someone willing to wipe out humanity—it isn’t as simple as just because “it was in his nature”, and I’d argue that’s an excuse Eren himself would use to try and rationalize his horrible actions.
That’s actually what Eren does the most with his all-seeing power: he uses it as an excuse not to take matters into his own hands.
What I feel AOT is criticizing here is that whether it was his nature, or his environment, or the generations of systemic abuse, how Eren dealt with his trauma was his decision. Eren perpetuating the cycle of trauma and hatred, of civilization and war, was his decision.
We later learn that Eren was the one who killed his mother, but I’d argue that rather than to only highlight that it’s in Eren’s nature to be free even if it’s a destructive goal, this scene also shows that trauma is self perpetuated—in the end, Eren literally caused part of his own trauma and led himself to a destructive path, though instead of being due to a decision that will have consequences in the future, it’s one that had consequences in his own past. Speaking of which, I think the mind-boggling past-present-future coexistence ability Eren attains due to the Attack Titan isn’t a coincidence, and perfectly complements his character: it’s the ultimate way to reinforce that he’s the one furthering his trauma through his pursuit of freedom, and that no matter where or why it started, he’s the one responsible for not dealing with it and harming everyone and himself so much.
This isn’t to diminish the fact that it was the world that shaped Eren to become that way, or to fall into a “good-victim” and “bad-victim” debacle. Putting it in the frame of the present day, I’d say that saying that your trauma is caused by yourself sounds extremely wrong and it’s not the point I’m trying to make. Yes, Eren causes his trauma, but only a part of it. Eren causes his suffering, but only a part of it. Whatever the case, it’s up to Eren to continue perpetuating that suffering for himself and others, or stop it, and unfortunately, what he ends up doing is continuing it.
Of course, asking for severely traumatized people to deal with their own trauma on their own is not realistic, is it? Asking for severely traumatized people to know how to not take it out in a violent way, without even being taught other ways, is unreasonable. For a quick view on my thoughts, even though I completely agree that Eren should be held accountable for his actions, in the end, the solution to his suffering isn’t to demand him to somehow know how to deal with it: that’s why others are key in helping heal that trauma.
So why didn’t Armin and Mikasa help Eren with his trauma, you ask?
Dude, they’re on like, the AOT equivalent to the 19th century. They probably don’t even know what trauma is, and they have their own to deal with.
Though the real reason is that Eren isolated himself from them, refusing to talk to them about his weakness—refusing to be vulnerable. They weren't allowed to be by his side, and that ultimately spells Eren's downfall.
But we know better now, don’t we?
In the end, I think that what the precious bond between the main trio highlights, whether they're conscious or not, is their ability to stand for each other no matter what kind of crueltry they experience. That’s what the Alliance’s last stand, and their ability to forgive and understand each other in the final arc showcases, too. That even if traumatized, we can make an attempt to connect with one another, and perhaps it will reach those who can’t even think of a way out.
That’s all it is about.