Read on Twitter
Thread: Eldia entered civilization sometime after the death of Ymir Fritz. Civilization, in the Spenglerian sense, means where systems of power have become automated. By the time of the manga, the Fritz government is the purest example of civilization.
One can look no further than the conduct of the military police. Because of this a nobility of money has replaced the nobility of blood (Ackermans being kicked out).
There is also the second religiousness as embodied by Pastor Nick and the Wall Cult.
At their core, the Eldian people are realistic, they've lost the idealism, they've become, in sense, barbarians. They're much like the Romans.
Hardened by constant warfare, humans lives are simply the cost for survival. Eldia is entering an age of Caesar's where this realism is shown fully. Erwin Smith is much like Julius Caesar or Cecil Rhodes. Realistic to his very core.
Spengler explains here and here.
He transforms the state and shakes its foundations, like Caesar did, yet he did not transform it into IMPERIUM. Eren Jäger, on the other hand, is much like Augustus. He imperializes the state and makes it into IMPERIUM.
Finally, we can also take note of the historical perspective of the Eldian people. They have some concept of past and present, but not future. Even when the walled city is cosmopolitan, there is not as much of a stark difference between the city and country (ie Feudalism).
If Eren is successful, Eldian civilization has entered into its final stages and will degenerate further. That is the unfortunate fact. However, as Achilles says, it is better to live a short life full of success, than to a live a long boring life. Destiny must be confronted.
