surprise in the narrative
Nope the first arc is the blackswords men arc, where Griffith is explicitly named as the enemy of guts, and guts is extremely vengeful towards griffith the reader/watcher does know that something is going bad was going to happen. The Golden Age arc is just kinda written so good that most people forget/suppress it.
Its kinda like the red wedding, where is a LOT of foreshadowing (very blatant via prophecy), but more so even because its actually a very large flashback.
It would be annexed by north korea, as it should have been.