There’s a Rumbling in Attack on Titan season 4 wherein you’ll witness Survey Corps and Eren Yaeger return from a devastating assault upon the Marleyan mainland and it cannot be Sasha’s stomach anymore. Eren managed to take out Marley’s military leadership and later, stole their War Hammer Titan by sneaking behind the enemy lines and inviting his allies to the party secretly.
Eren also managed to capture the owner of the Beast Titan, Zeke and this is certainly a landmark victory. However, a few of his friends are in disagreement about whether such a kind of direct battle was needed or whether it was the wisest decision all this while. Everyone seems to have their own perspective and agenda to present in Attack on Titan season 4.
The final moments of Attack on Titan season 1 presented the first inkling of the Rumbling when a Titan’s face was shown to us inside Wall Sina and it was subsequently revealed to us that all the three giant circular walls were constructed from millions of hardened, massive Titans on Paradis Island.
It has been known that King Fritz built these walls after evacuating to Paradis Island with the help of the power of the Founding Titan. This information was provided in the history lessons provided by Grisha Yaeger and Willy Tyber.