So, the story so far:
A long time ago, a women named Ymir Fritz made a deal with the Devil (I'm sure that there's more to that), she received the titan powers and when she die her "soul" (I think that's her power) descended to 9 titans and those titans founded the Erudian Empire. The Erudian Empire destroyed the Maray Empire and then they became the new rulers. The Erudian people started getting very xenophobic ideas about the other clans and they started treating them like inferiors and then they started killing everyone who wasn't a true Erudian. (it's interesting, since this is almost similar to Nazi Germany with the Aryan race).
So what's left of the Maray Empire actually managed to organized and get stronger from within and they rebelled against the Erudian Empire and thus, the Titan Wars started. Maray Empire won the war and they managed to get at least seven of the Nine Great Titans. For me, these "great titans" are actually powers, like the crystallization, steam, armor, etc. So the Coordinate power is one of the two left IMO.
While the Titan Wars was happening, a man known as King Fritz decided to built a safe place from the war, a place where he built three giant walls and gave the Erudians the option to flee and stay safe there, this place was called Paradi Island, which is obviously where Eren and everyone else is at right now.
Time passes and we have Grisha living on the Maray Empire, as we can see, the Maray Empire created a place where all the remaining Erudians could live, nevertheless, they were treated pretty bad because of their history and Maray citizens see Erudians as descendants of the Devil (you know, Erudians come from Ymir Fritz, who made the deal with the Devil). So that explains why Annie, Bertholdt and Reiner refeir to the people on the walls as demons, even though it's very hypocrite of them since they are also Erudians with the title of Warriors who work for the Maray goverment.
At the end we finally discover what are the Titan Shifters and why they are attacking Paradise. While Grisha, who joined the Erudia Revivalist movement, plans to get the coordinate to controls titans and start another war for their freedom, the Maray goverment creates the Warrior program, a program with the goal of recruiting very young, smart and talented Erudians that will have access to the seven titan's powers and their mission at that time was to attack Paradise because apparently King Fritz declared war on them.
But then Grisha founds out that this is a lie thanks to their "spy" on the Maray goverment and apparently the Maray goverment's true mission is to look for fossil fuels. Grisha then decides to offer his son Zeke (THE BEAST TITAN!!) to the Warrior program so he can be their spy and that ends up biting him in the butt since then Zeke tells the Maray goverment aout Grisha's plan and the people involved in this plan are sent to Paradise, where they become mindless titans.
So that's a small summary, sorry if it has some grammar errors. Also, I'm pretty sure that the Maray goverment's goal changed once they found out Grisha's plan and then they decided to capture the Coordinate.
So if you think about it, the titan shifters are still jerks who work for an evil goverment, but at the same time, Grisha's group are also jerks, since they want to repeat history and kill every Maray citizens since they are superior. So the scouts are stuck in a very difficult situation, so I wonder what they plan to do once they understand the big picture.
Edit: Also, this was DEFINITELY, an amazing chapter, so far I love where the story is going.