WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 28, "The Dawn of Humanity," now streaming on Funimation, Hulu and Crunchyroll.
Willy Tybur wasn't exaggerating when he proclaimed that the Rumbling would mean the end of Attack on Titan's world. In the Final Season: Part Two's finale, the Rumbling officially made landfall in Marley and Eren Jaeger's army of Colossus Titans proved to be entirely unstoppable. While the Scouts and Marleyans who've teamed up to stop Eren have discussed whether they should kill him, that might be impossible now that the series has given its first up-close look at how the Rumbling is being carried out. The greatest force humanity could muster did nothing to halt or even mildly inconvenience the Rumbling as the Colossus Titans swept past their blockade, leaving destroyed ships and charred corpses in their wake.
The entire reason Marley decided to restart the war with Paradis Island at the beginning of Attack on Titan was that modern weaponry was overtaking the power of Titans. For 100 years, Marley used their Titans to conquer neighboring countries as they expanded their empire. However, more recently they had been losing territory as weapons began to appear that could negate the threat posed by Titans on the battlefield. Marley began to fear the end of Titan dominance was upon them, but the Colossus Titans that make up the Rumbling have proved Titan dominance is a long way from over.
In "The Dawn of Humanity," the entire world outside Paradis Island banded together and pooled their resources to assemble a fleet of the most powerful weapons currently possessed by mankind. While their barrage of missiles did succeed in eliminating a handful of Colossus Titans as they swam across the sea, the fleet was ultimately helpless to stop them and swiftly obliterated. The Colossus Titans used the powerful waves from their rapid swimming to toss the boats into the air, and the steam they gave off instantly incinerated anyone who had the misfortune to be exposed to it -- which was everyone on the ships.
When one Colossus Titan was killed, several more took its place, resulting in no discernible difference in their numbers once they passed the fleet and made landfall. The land-based weapons on the shore weren't powerful enough to harm them, and their march to flatten the Earth officially began. Humanity is now officially defenseless in the face of the Rumbling, and the only other people who might stand a chance at stopping Eren have still not begun their actual pursuit. Now that the Colossus Titans have proved to be unstoppable, Mikasa's preference to talk Eren down rather than kill him might be the only realistic option.
Eren's new Titan form is more than double the height of the Colossus Titans and its overall mass is incalculable. Surrounded by the most powerful Titans in the world and possessing an incomprehensible Titan body himself, anything short of the near-nuclear explosive power of Armin Arlert's Colossal Titan is useless -- and even that may not be enough. It's unclear what the Scouts and Marleyans plan to do once they catch up to Eren, but the only thing that's certain is that it will be the fight of their lives just to get past Eren's army of Colossus Titans.
The speed and power of the Rumbling means a significant portion of the world is certainly doomed, regardless of how quickly the Scouts and Marleyans catch up to Eren. The outside world's soldiers fled in terror at the might of the Rumbling, and once our own heroes witness the devastation firsthand, some may join Annie in the all-hope-is-lost-so-why-bother department. After the announcement that Attack on Titan, The Final Season: Part Three won't premiere until 2023, it's going to be a long wait to see how (or if) the Rumbling is stopped, considering an all-out assault against the Colossus Titans has already failed miserably.
