who read The attack of the giants or watched the anime, knows that there are several references to Germanic peoples and Germanic culture. Just think of the names of all the protagonists, clearly German. However, after passing the walls and reaching the sea, these references expand thanks to some revelations.
As explained with Ymir's past, there is a special relationship between two races, the Eldians and the Marleyans, that unleashed much of the hatred currently present in Attack on Titan. Clear references to Romans and Teutons and more. Hajime Isayama deliberately used these two races as a reference for his manga? Apparently yes, as he himself explains.
During an interview with Crunchyroll, the author was asked if the real events influenced Attack on Titan. "I think the story is more believable when there's some truth to it. So when the idea of drawing the world's point of view came to me - for example looking at the map, I turned it on its head respecting the real world for something similar but different. People can understand the context without having to explain everything. For example Eldians and Marleyans. They really resemble what Germans and Romans were 2000 years ago. It's kind of an unwritten rule that I use in my stories."
The world of The Attack of the Giants is actually inverted with respect to ours on both axes, and the resemblance of the Eldians to the Germanic tribes and the Romans to Marley's army has been emphasized several times. But now comes the confirmation of the author, who reaffirms this concept.