Eldians and Marleyans are two main nations introduced in the story.
The Titan Curse started with Ymir.
Her daughters consumed her body to preserve the Titan Curse.
Marleyan were the ones sending Pure Titans to Paradis, where Eldians lived.
Despite Attack on Titan (Shingeki no Kyojin) not having the most intricate lore, it's still pretty easy to confuse some of the viewers. And this is exactly what the anime did back when Season 3 finished airing. And kept doing it in the Final Season. So let's look at the series' world and discuss a couple of things.
Eldians and Marleyans
There are two nations that are represented in the series the most: Eldians and Marleyans. Only the first ones are capable of turning into titans, be it a Pure Titan (the one who has no consciousness) or a Titan Shifter (those who turn into a titan and back).
All Eldians are descendants of Ymir, who is the founder and the first Titan Shifter that ever existed. After her death, the king forced his and Ymir's daughters to eat the woman's body, and that's how the power of titans was preserved. Eventually, the powers would split further into the individual Nine Titans, which only the descendants of Ymir (or Eldians) can possess.
Such characters as Gabi and Falco are also Eldians, even though they live in Marley. The blood is what matters, not the place of residence.
Titan war and Paradis
Paradis is the island where the story of Attack on Titan starts. The one where Eren and Mikasa lived.
Years ago, there was a war over the Nine Titans on the continental mainland, but the Eldian King Fritz chose to abandon the conflict and move the capital to the island of Paradis. He gathered as many Eldians as he could and transferred them to the island.
He used the Titan Power to build three walls there. That's why there are Colossus Titans inside of these walls. And these are the titans that Eren freed when he started the Rumbling.
Marley and Pure Titans
Marleyans knew about Paradis and were scared of the Titan Powers, that's why they wanted to put an end to Eldia and Eldians. They turned them into Pure Titans as punishment and sent them to attack Paradis.
That's why Paradis was constantly under the attack of titans, and that's where all of them came from. However, Paradis Eldians didn't know it back then.
Everything became clear only at the end of Season 3, when the Survey Corps found Grisha's notebooks. They learned about the existence of Marley and other people outside of Paradis. That's also how they realized that Pure Titans used to be Eldians before, who were turned into monsters against their will.
It's not the most difficult one, don't worry.
Summary:
Eldians and Marleyans are two main nations introduced in the story.
The Titan Curse started with Ymir.
Her daughters consumed her body to preserve the Titan Curse.
Marleyan were the ones sending Pure Titans to Paradis, where Eldians lived.
Despite Attack on Titan (Shingeki no Kyojin) not having the most intricate lore, it's still pretty easy to confuse some of the viewers. And this is exactly what the anime did back when Season 3 finished airing. And kept doing it in the Final Season. So let's look at the series' world and discuss a couple of things.
Eldians and Marleyans
There are two nations that are represented in the series the most: Eldians and Marleyans. Only the first ones are capable of turning into titans, be it a Pure Titan (the one who has no consciousness) or a Titan Shifter (those who turn into a titan and back).
All Eldians are descendants of Ymir, who is the founder and the first Titan Shifter that ever existed. After her death, the king forced his and Ymir's daughters to eat the woman's body, and that's how the power of titans was preserved. Eventually, the powers would split further into the individual Nine Titans, which only the descendants of Ymir (or Eldians) can possess.
Such characters as Gabi and Falco are also Eldians, even though they live in Marley. The blood is what matters, not the place of residence.
Titan war and Paradis
Paradis is the island where the story of Attack on Titan starts. The one where Eren and Mikasa lived.
Years ago, there was a war over the Nine Titans on the continental mainland, but the Eldian King Fritz chose to abandon the conflict and move the capital to the island of Paradis. He gathered as many Eldians as he could and transferred them to the island.
He used the Titan Power to build three walls there. That's why there are Colossus Titans inside of these walls. And these are the titans that Eren freed when he started the Rumbling.
Marley and Pure Titans
Marley territory map in Attack on Titan
Marleyans knew about Paradis and were scared of the Titan Powers, that's why they wanted to put an end to Eldia and Eldians. They turned them into Pure Titans as punishment and sent them to attack Paradis.
That's why Paradis was constantly under the attack of titans, and that's where all of them came from. However, Paradis Eldians didn't know it back then.
Everything became clear only at the end of Season 3, when the Survey Corps found Grisha's notebooks. They learned about the existence of Marley and other people outside of Paradis. That's also how they realized that Pure Titans used to be Eldians before, who were turned into monsters against their will.