Eldia

Erudia (エルディア) is the nation occupied by the Subjects of Ymir or Ymir's People (ユミルの民). In ancient history they dominated the world, until a century ago when the Titan War isolated many of their people in the walls.

History
Over 60 years before the fall of the Shiganshina District, Ymir was cast out by her people, who "hated her just for existing". She would wander outside the Walls for 60 years until the fall of Wall Maria in the year 845. The Hometown, a society outside of the walls, sent Reiner Braun, Bertolt Hoover, Annie Leonhart, and Marcel to breach and invade the southern gate of Shiganshina. On their way to their mission, Ymir, as a Titan, stole the power of Titan shifting from Marcel after catching and consuming him while he tried to defend his friends. After this, Ymir regained her conscious mind and became a part of the society within the walls.

Ilse's Notebook
In the year 848, Ilse Langnar of the Survey Corps became the last surviving soldier of the left flank of the 2nd brigade during the 34th Expedition, lost in Titan territory within Wall Maria. With her Vertical Maneuvering Equipment broken and horse missing, she chose to record her experiences as she made her way north toward Wall Rose. During her journey, she is caught by a Titan who forces her back against a tree but refrains from eating her. The Titan speaks to her, first believing her to be "a subject of Ymir" before mistaking her for "Lady Ymir" herself. Ilse attempts to communicate with the Titan while taking notes, asking what it is, where it comes from, and, after losing her composure, furiously asks why they eat humans. The Titan only responds with pained moaning and later starts ripping off its cheeks when Ilse screams at it. When she attempts to flee, the Titan catches her and crushes her head between its jaws (while taking notes until her last breath), but does not consume her body. Her notebook and remains were discovered a year later by Hange Zoë and Levi Ackerman.