In the beginning, humanity was inside the walls, a handful of people trapped between 50-meter giants to protect themselves from the threat posed by the mysterious giants. With the arrival of Eren Jaeger and his friends in the Legion of Exploration, the world of The attack of the giants it began to change by expanding dramatically.
This has brought some secrets to light, such as the origin of mankind, or rather the people of Ymir. also known as eldiani. But who are these characters from The Attack of the Giants? Some of these events are covered in chapter 122 of the Hajime Isayama manga. So if you don't want spoilers, don't read any further from the next paragraph.
Their origins go back to bygone times, more than 2000 years ago. At one time, the Eldians were a barbarian tribe struggling to conquer more and more territory and battling with the Marleyans. The arrival of Ymir and the power of the giants radically changed the balance of power in the world. allow the Eldians to prosper to the detriment of others.
However, the Marleyan coup and the recapture of the Kingdom of Eldia were mandatory King Fritz moves to the island of Paradis where he took some of his people. All Eldians, descendants of Ymir and thus of his blood, can be controlled by the power of the founding giant. In return, they lose their memory and are convinced that they are the last people on earth, until the discoveries that were told in the third season of The Attack of the Giants.