Ehm, about going to nations... I'm not sure I understood the problem. The game works this way:
You can advance to neighbour nations of the one you currently are. But once you advance to a new zone, you are not allowed to go back to "conquer" a nation you didn't visit. You can visit Nocverchis, then Eldrien and after that advance to Zone 2 and visit Fernia, for example (Fernia is a neighbour nation of Eldrien).
It's basically that mechanic. Hope this explanation helps. If it didn't work like that, you could have probably broken the game with an old save.