HEAVY SPOILERS FOR AOT
Basically, Eren and the cast are descended from Germanic tribes that then formed an empire that eventually fell apart. Only those who are descended from this tribe can turn into titans.
The empire fell apart cos a certain other nation ‘subverted' them -

-from within. Sounds familiar like what Hitler accused the Jews of doing . This wouldn't have worked if the current emperor wasn't ‘compromised’ by a pacifist king but luckily for the other Marley he was. Sounds like a criticism of pacifist beliefs of current Japan and Germa-

to me .
Some of the descendants of the tribe were exiled to the AoT's equivalent of Madagascar, while the rest are left on the main continent where the other Marley now holds power. Eren and co are from the Madagascar equivalent whereas Reiner and the other warriors are from-

-the continent. The descendants of the tribe are taught by Marley that the sins of their ancestors (basic imperialism as well as many other atrocities such as rape/ ethnic cleansing) are their fault and that they are to atone for it. They brainwash children like Reiner and co to-

-fight their wars for them. Ironically enough Marley uses the descendant’s power to turn to titans to fight their wars and form their own empire. This leads to an increase of global hate towards the descendants. This is one of the many things that certain groups such as the -

-alt right accuse Jews of doing . Seems to be that Isayama agrees with their sentiments in regards to Japan and perhaps even Germany. Disappointing to see such blatant anti-Semitism.
Once Eren and co learn about the truth of the outside world, they infiltrate the Marley when-

they have a meeting with important officials from all over the world. Those officials then declare war on the Island cos Marley focuses the hatred of the world on them. Eren then unilaterally attacks the nation leading to many civilian and military officials dying. The other-

members of Eren's team didn't agree with him but were forced to join too to make sure Eren escapes.
Shit happens (a literal fascist militia is formed) and then the world is getting ready to destroy the Island in retaliation. Eren prioritises the lives of his people over the-

rest of the world so he is activating the rumbling (freeing the hundreds of thousands of 60+ meter titans in the walls to trample the world flat). Basically, he is willing to commit global genocide to protect the existence of his people and their children (1488 ). Eren's side-

is portrayed as sympathetic cos he cried... There’s even statements by Isayama showing that he even feels sympathy for depraved characters such as Floch and that he’s an 'audience self-insert' ( https://yaboylevi.tumblr.com/post/185863098141/shingeki-no-kyojin-story-guide-isayama-senseis)/ ( https://fuku-shuu.tumblr.com/post/162652398937/snk-news-isayama-hajimes-bessatsu-shonen-august)

TLDR: AoT is fascist and an immoral fictional story where many of the principles of the alt right and white nationalists are justified and even glorified (“GIVE UP YOUR HEARTS!”)