The Bastion of Ethylia
During the beginning of the year 4239, in the Long Reprieve, several nobles decided to claim land that adventurers had already taken in Kurth. The adventurers were paid well and sent off elsewhere while the nobles began a long process of creating their new city, Oslo.
When civil war engulfed the Middle Lands a large amount of citizens fled to Oslo which transformed the city overnight. The most problematic part of the city was that to the West there was a mountain chain perpetually covered in fog which no explorer ever returned from. That, and the dead barrow-lands to the south were the only geographical problems until 4817.
A few of the prominent lords of Oslo sold their family titles in exchange for immortality and vast material goods. The Demon Lords eventually opened a portal that would, for one hour each day, open and allow demons to pour out into Oslo. This was allowed by the rest of the non-demon lords with excessive bribes and gifts with assurance that the demons wouldn’t be able to rise in any political sort, nor would they be allowed to openly declare war against any Oslo citizen.
For a while, this agreement benefited the city of Oslo. The roads became safer, wilderness was cleared and stayed clear while people settled, and even the barrow-lands were explored to some extent. Eventually, though, the demon population had tricked or stolen all the land and titles that the human lords of Oslo had, making them the ruling class. When that occurred, all demon city guards were issued back into their abyssal portal and the people of the city came to flock back to safety, though at a heavy cost.
Discrimination against non-demons was high, and the city remained as such until 5382, when the Demon Lords of Oslo declared war against the Middle Lands and were almost immediately brought to ruin, both from the war overseas and back in the city where a long-standing revolution sparked.
In four months the city was destroyed and it was revealed that mind flayers had been working in tandem with the Demon Lords. One final pact was made by an adventurer who was leading the charge against the demons. The pact itself is unknown, though many stipulate it was what caused the sudden change in the demon presence, the lack of safety for demons and tieflings in the area and the overgrowth and climate change that occurred in the barrow-lands south of Oslo. Many people flee into the newly-created wilderness, becoming farmers or bandits or die.