I think it was 900 years past, Eldians received Titan power, and after time, grew into conquerors. They warred with everyone, until Marley finally took them down by stealing some of the Nine. Marley then basically Nazi-ed Eldians for multiple generations, forcing them into segregated communities with limited rights (like modern-day Israel has with Palestinians).
Before that happened, half the royal Eldian bloodline and race fled to the island (which became the setting for the story up to this point). That's why the Beast Titan was able to turn Connie's village into Titans. Basically, every person on that island, living within those walls, has the potential to become a Titan, but the Royal family (Christa/Historia Reiss's family) used its powers to wipe the people's memories, changed their names, installed a fake royal family, then formed a religion which guarded their secret and misled their followers. But thanks to the threat of Marley's Titan-Shifters (Annie, Bertoldt, Reiner and Zeke, specifically), Historia pushed back against her family, who had shunned her for legitimacy reasons.
So:
Eldians were blessed by a goddess and started good, then turned bad.
Marley was the hero country to defeat them, then THEY went bad, too.
Titans are ALL Eldians, but the mindless ones are created by injecting the spinal fluid of the 9 into "criminals" as punishment... all the Titans you saw horribly eating people are basically on an island prison for fighting back against Marley's abuse... and sadly, are serving as a cruel joke - being forced to mindlessly kill their own people in a way that their founding fathers had once done to others.
The rest of the world hates the Eldians, and the.defectors hated themselves. The peaceful wanted nothing to do with war, but were still lumped in; however, with the Eldians essentially having been isolated/domesticated, the rest of the world now hates Marley, as they went on to abuse their new found power to take over land & resources.
. Đi cả trăm mạng mà về có 9 mạng. Zeke chỉ được cái to xác với điều khiển Titan khác, gặp Levi chưa đến vài giây là xém chết rồi 
... Ackerman hơi bị impa.