In The Exiled: Of Shade and Shadow, Astra and Louko travel through what is called the Merym Pass. This is the least perilous way through the Rheritarus Mountain range which divides Nythril from Merimeethia. The excerpt below is where Louko explains how the countries Merimeethia and Nythril came to be:
"[Nythril and Merimeethia] were one country a couple thousand years ago. Dragons and humans lived together. There were two in particular that were fast friends—Merym and Nythrian. The records are rather… torn on what happened, but It seems the human Nythrian turned on the Dragons and demonized them—especially Merym. There was much bloodshed, and the countries ended up being created in the split. Nythril still hates Dragons to this day.”
The pass itself is a result of the climax in the bloody conflict, and serves as a permanent memorial and burial ground for the casualties from both sides.