I’ve seen a lot of people connecting it to the Irish Civil War, but I think there’s a lot in there about the inherent selfishness/social-push-pull of creation (of art, specifically).
I don't think there's any allegory at all. The Civil War is a bleak backdrop, a reminder of brotherhood turned to hatred and the impending threat of death and so forth, but it's not much more than that. It's connected to the story by aesthetics and by mood rather than by plot or by meaning.