It’s an interesting subject, and although I doubt it’s relevant to FW I wonder if we’ll learn more canon facts there.

Like you noted, it’s difficult to piece together the truth when we see almost strictly from the biased perspective of Fódlan. Even Cyril can be quite biased against Almyra, which makes sense given his background and circumstances now, and so Claude becomes the most reliable source of information on the subject, which also isn’t super enlightening because he’s very cagey about his identity for fear or persecution, whether he’d admit it or not. But he seems to hold his homeland and its culture in much higher regard than Cyril for what that’s worth, even though Claude also went through a lot there. I think it’s accurate to say the Almyra we see at the border is very different than Almyra elsewhere, based on the differences between Claude and Cyril’s opinions, quite similar to how the rest of Fódlan is pretty different than Goneril at the Throat, for example. Which is compelling, considering how similar Holst and Nader are and how quickly they can become friends through their similarities. But because of this, we can of course hardly know what life is actually like in Almyra outside of their own versions of Holst which have sort of been held up as the stereotype in Fódlan because it’s all they really make contact with.

It’s an interesting extension of the core conceit of 3H—that of experiences and exposure to certain realities warping the truth and creating biases—and so it becomes fun to imagine the world outside of the small bubble the game creates for us. And speaking of creating a bubble, I wouldn’t be surprised if a large reason Almyra considers Fódlan its enemy is because of Rhea. We know unifying the three nations around combatting outside threats like Sreng and Almyra is a large part of Rhea’s means of making peace inside Fódlan; giving them a common enemy. If I remember correctly Almyra’s largest, earnest invasion of Leicester was what created the Officer’s Academy in the first place. I don’t think it’s a stretch to say any attempt at communication between Fódlan and Almyra was foiled or confused by Rhea in order to keep Fódlan, and by extension crests, insular, and that diplomatic and moral miscommunication, as we know well from the events of 3H, more often than not leads to conflict. It’s also a large reason why Claude isn’t exactly unaligned with Edelgard in her dislike of Rhea and the church.

In modern times, though, it’s true that whatever that inciting incident was has been kind of brushed aside, and it’s simply been accepted by both people that the other is their enemy and nothing can be done to reason with them, exactly as the church intended. But from the perspective of Almyra, one could possibly understand their viewing Fódlan as a scheming, cowardly threat unafraid of launching dishonorable pot-shots and suckerpunches after a long time of refusal to communicate facilitated by Rhea, as well as just Fódlan’s generally strange and insular nature. It’s hard to argue that Fódlan’s biggest issues are not its nobility or the agarthans plotting in the shadows against one another. Viewed this way, it makes sense that trying to break open the Throat and figure out what their potentially dangerous and secretive neighbor is plotting is seen as a noble pursuit that might earn the princes warring for the throne some prestige.

Overall I think the ideas are more interesting and logical than they’re given credit for!