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.
In the fifth episode of Attack on Titan's fourth season, the anime's own 'endgame' is finally revealed and its consequences, as you'd expect, could be disastrous. As Willy Tybur gives his declaration of war speech, he also goes over the true history of the Eldian people and their relationship to both the Titans and Marley.
It's not until he reaches his final piece of information, however, that he provides his audience with the main incentive to start the war -- the Rumbling. He goes over it quite briefly but awards the blame for this possible event to the one and only, Eren Yeager. So, what is the Rumbling and how is it really linked to Eren? Let's get into more detail.
In Season 4, Episode 5 "Declaration of War," Willy Tybur gives a big speech to an audience of military leaders and other diplomats in Marley's Liberio. In it, he explains that when King Fritz took the Eldians to Paradis Island and built the walls, he sent a threat to the mainland, pledging that if they were threatened he would unleash "tens of millions of Titans" upon them. This threat was enough to keep them from ever pursuing King Fritz and his people. But as Willy goes on to say, that was never his real intention.
Where would these thousands upon thousands of Titans come from? From within the very thing that has protected the citizens of Paradis for a century -- the walls. Willy Tybur touches upon the creation of the walls in his speech as well. He explains that King Fritz used the Founding Titan's powers to summon innumerable Colossal-like Titans that lined up shoulder-to-shoulder and hardened, forming the three walls we know today. It is this almost incalculable number of Titans that would be unleashed in the Rumbling.
How does this connect to Eren Yeager, then? Well, as Willy bluntly tells the audience, he is the new owner of the Founding Titan. This means that, if he so chose, he could unleash the Wall Titans and set the Rumbling in motion. Therefore, the fate of both Marley, and potentially the world, rests in Eren's hands.
The Rumbling, if unleashed, would be an apocalyptic event. Think about it: when the Colossal Titan kicked a hole in the wall at the very beginning of the anime, it was absolutely horrific. The sheer size and strength seemed enough to topple mountains. Now imagine tens of millions of these Titans, able to crush entire neighborhoods or even cities in a single footstep. If Eren unleashes the Wall Titans, the entire world would be at stake.
In addition, by releasing the Wall Titans, Eren would be sacrificing the safety of his own people -- the Eldians on Paradis Island. The disappearance of the Wall Titans would mean the walls themselves would be gone, leaving its civilization open for a Pure Titan or human-led attack. Now, we still don't fully know what has happened on Paradis since the end of Season 3, and four years have passed since then in the anime. But unless the entire population of Paradis is in support of Eren, he will be at fault for the endangerment of his own community as well.
Willy Tybur was smart to use the Rumbling as his incentive to declare war on Paradis Island and its Eldian citizens. What could possibly be a greater motivator for war than the potential destruction of millions of people, if not entire nations? Should Eren choose to utilize this tactic, he will be heading down a path he cannot return from. With most of the season left to go, we'll find out just how far Eren is willing to go to keep moving forward.