@Asta All of those points come from Marley's propaganda, everything that the world knows from Paradis island comes from Marley, including what the Eldians from the continent know about, and Marley is a country that is already at odds with the world and that is a few years from losing their military advantage.
The moment people who went to Paradis island gave themselves the opportunity to learn what was actually going on is where the alternative happened, but instead of opening that door and increase diplomatic actions, they bite on Marley's bait and confirmed their narrative by attacking the conference. Even after doing that they still had allies on the inside, they still could have used that to their advantage, but they didn't, they could have taken Marley's role on the global conflict by exposing how Marley was lying in order to defend their own interest.
Also there's a great reason for the other countries to refuse Marley's offer, not only where they lying, Paradis Island was no longer planning world conquest, but the Rumbling turned out to be real, they could have come to an agreement to cooperate with Paradis Island while they developed their own anti titans weapons, the oportunity alone of being able to buy time in order to avoid being defenseless is worth refusing Marley, while Paradis Island could have used that time to fostered better international relations to the point that the conflict wouldn't have been needed, but that didn't happen either.
Those are the alternatives, you don't even need to count on the good will of others you just had to use what they had, factual information and an actual superior military powers based on magic.
@Harjeli I get you but realism is not always a good thing to have i fiction, and i don't think the author is going for a realistic portrayal of a human in here, i think that doing something like that this late in the game is not only pointless but irresponsible.
Realism quite a niche thing that hardly ever works in fiction, because reality doesn't has to answer to consistency, for example in reality Australia had people become toilet paper robbers because they hoarded TP in a panic and ran out of it, if you put such an event in a serous story that has been known for characters answering to a narrative logic in a fantastical setting, then it would become a gag.
For a fictional work narrative consistency is more important than realism, If the author is gonna show Eren having feelings of guilt for things that he has yet to do, i want the story to address that and build upon it, i want the story to explicitly answer what was happening there, and tell me if Eren was genuinely conflicted and is deluding himself thinking that this is the only way (in which case this means that he can probably be talked out of it if someone presents him some other options), or if he was just being an hypocrite and never meant any of that (in which case he will just keep doing what he is doing, but should have never apologized for it, since he wasn't being genuine about it in the first place), or if something else was going on.
However if we are aiming for realism, the author doesn't has to do anything with it, he can just write it off as something that happens because humans are that way and never touch on it again, it was just a phase that happened once, and that was all there was to it. With realism some things just will happen and they wont have any impact to a story, real lief has filler, real life does not care about consistency.
War and Peace is a novel with a lot of realism, it is probably the one novel with the most realism out there, and it is plagued with stuff like that, it is a struggle to read because every character is realistic, probably 80% goes nowhere, just like in real life, it is a bunch of biographycal events, and developments made into a story taken from interviews, people just exist, and that's important, and is what the novel is known for, it makes you appreciate the meaning of the meaningless, the purposeless, the death ends that go nowhere, the plot lines that don't pay off, the events without connection, because realism is like that, is about the side characters that have little to no impact on the story.
But this manga is not a realistic story, it has mature themes, it has gruesome themes, it has a somber tone, but is not realistic, nor its characters nor its events aim for realism, if we are going to push for realism now, then how can we know what is important to note and what is just a quirk product of realism?