Nyn moves troops to the unoccupied territory in the north. You were warned to not expand here. Stand down or we will declare war.
Conservatia requests that it at least be allowed to use the region to move through the region to settle the north-eastern coast, which is the sole reason of its eastern expansion.
Further-more, you have no claim on the region, as they were forfeited.

As said, you cannot reclaim them for another 10 years, and with such a statement it is only logical you have no claim on them at all for these ten years as well, as they are not your lands.
Conservatia, however, has de jure claims under the pretense that it is the child nation of a former empire that resided in the region, and it's natives are on the former Conservatian empires soil.
Conservatia has no interest in peaceful expansion. They are not hungry people - they are warmongers. Take a look at their country and see that they have no interest in feeding their people.
EDIT: Actually forgot to put this in, but the reason we're going for the coastal lands is for fish. Conservatia asks that you redirect your misguided assumptions.
On a OOC note, backstories are good for viable de jure claims.