WARNING: The following contains spoilers for Season 4, Episode 5 of Attack on Titan, "Declaration of War," now streaming on Crunchyroll, Funimation, Amazon Prime and Hulu.
For the majority of Attack on Titan's run, Eren Jeager has been a typical vengeful hero. As a young boy, he witnessed his mother being eaten alive in front of him and his home torn apart by invading monsters. This spurred him to join the military and swear an oath to destroy every last Titan alive -- a pledge that became more complicated when the human origin behind the hungry creatures became apparent.
The anime's third season ended with Eren at a crossroads. And, as of Season 4's Episode 5, it seems that one of Paradis Island's leading lights in the war on Titans has dimmed significantly, turning the rage he once felt so intensely for the very things he can transform into on others like him in Marley, the island's greatest enemy. At the end of the most recent episode, Eren, following a tense exchange with Marleyan Warrior Reiner Braun, his duplicitous former comrade, brings the fight straight to the heart of Reiner's motherland -- bursting out of his hiding place as the Attack Titan and brutalizing Willy Tybur, the man who just declared war on Eren. The question is: how justified are Eren's extreme actions? If at all?
Let's look at the argument in his favor first. No matter what Eren did or didn't do, Marley was on the warpath back to Paradis Island anyway, so arguably, Eren is merely dealing a preemptive strike. Plus, as he reminds Reiner, this has been a long time coming, specifically citing that fateful day that he lost his mother on, which Reiner directly caused. If the last few episodes are anything to go by, coupled with Willy's recap of centuries of Marleyan-Eldian fighting, Marley will likely never be satisfied to leave the island alone until it recovers the Founding Titan, which Eren currently has.
The Tyburs would stress that the Founding Titan is a WMD that until now, was safe in the hands of the royal Fritz family after King Karl Fritz embedded his peaceful will into it 100 years ago. In Eren's hands, however, there's no guarantee how and when the Founding Titan will be used, with the catastrophic Rumbling being the worst-case scenario.
Even with this and Eldia's imperial history in mind, it can't be denied that Marley itself has caused immeasurable suffering to its past rulers, cultivating an oppressive culture of self-loathing and racially-motivated servitude among the Eldians who live there, definitely making them, in more recent history, the more villainous side. However, Willy Tybur's speech in Episode 5 reveals that Marley was unaware that King Karl Fritz had put measures in place to keep the Founding Titan caged and erased his peoples' memories, rendering them ignorant enough of the outside world to reignite the Great Titan War again.
This, along with knowing what Marley fears the Founding Titan is capable of, goes some way to make its invasion of the island at Attack on Titan's start more understandable, but an infiltration mission of that magnitude with that many civilian casualties speaks less to the nation's desire to disarm the island than it does to its aforementioned hatred of the "devils" who live there. You only have to look at Marley's decades-long program of forcefully turning Eldian criminals into mindless Pure Titans and pointing them in the direction of their countrymen to appreciate how aggressive its racism is.
In this light, Eren (and his hiding allies) plan to eliminate Marley's Warriors -- and possibly retake the Shifters in their control -- could be viewed as one designed to simply eliminate the most immediate threat to their home once and for all. It's not about spilling Marleyan blood for revenge's sake -- it's a tactical strike. The emotional component, too, is hard to forget. Eren has only ever known a life of Titan attacks and walls. Finally seizing control of all the chaos is a logical desire.
This brings us to the counterargument. Unfortunately, we know from the preview of the next episode that a lot of Marleyan and Eldian civilian blood will be spilled, and it should be noted that Eren is specifically attacking Liberio, Marley's internment zone for Eldians. This is sort of unavoidable given that it's where the Warriors are based, but it puts Marley's Eldian community directly in the crosshairs all the same, which Eren shows no qualms about.
Eren explains this to Reiner as: "We're the same," meaning that during his time behind enemy lines, he's seen that there are good and bad people there, a moral complication that he knows Reiner himself experienced on the island. And just like Reiner, Eren is doing what he thinks needs to be done to save the world. The difference is that while Reiner has been left utterly broken by the experience and looking for an escape, Eren feels more emboldened than ever to kill those who have wronged him. He's choosing to be the villain that Willy paints him as. Eren could have attempted to work diplomatically with Willy as the former King a century ago did with Willy's ancestors; instead, he's chosen to continue on the vengeance path. "I have to keep moving forward."
If you're finding all of this to be an absolute moral minefield, it's because it is. Attack on Titan offers no easy answers and its lore is steeped in some pretty murky and controversial subject matter. The clearest lesson here is in Willy's own speech: nothing will change in this cycle of violence until someone finds the strength to break it. The reason why the Tybur and Fritz families' plan fell apart was that they were the only ones in on it. Marley was never going to forget the Eldian Empire's sins and the Eldians on Paradis Island were always going to yearn for freedom from their gilded cage. Ultimately, Eren has only ever known one world and that's his island -- that could be the only one he plans on actually saving.