Abelion Hills

Abelion Hills (アベリオン丘陵) is an area of wilderness with vast hills that lies between the Slane Theocracy and the Roble Holy Kingdom. It is inhabited by all kinds of demi-humans who are constantly trying to invade the Holy Kingdom. Jaldabaoth conquered the region and ruled over it until the Sorcerer Kingdom laid claim to the territory.

Background
According to the Web Novel, in the past, this area was once home to a kingdom of hill dwarfs, but it was later destroyed by demi-humans. After that, it became a lawless area where a myriad of demi-human tribes fight day and night for control.

There were all kinds of demi-humans in the hill region, yet they did not have good relationships with each other. Rather, they often fought over territory, and apart from cases where Ogres took Goblins as slaves and cruelly used them, these races very rarely worked with each other.

The constant warfare and dangers these demi-human races produce is so troubling that the Roble Holy Kingdom constructed the largest and longest wall barrier on the continent to keep them out. The Slane Theocracy have made ​​numerous attempts to subjugate and cleanse the area, but so far its efforts have only managed to temporarily thin the demi-human population.

In the past, the Adventurer's Guild of the Re-Estize Kingdom had sent people there, but none have ever returned in one piece. As a result, the area is completely unknown terrain to the kingdom's citizen.

One of the most influential demi-humans to come from this land is Buser, also known as the King of the Demi-humans. Buser was a Bafolk famed for his strength as he managed to unite all of the Bafolk tribes under him as well as conquering many other demi-human tribes in the region.

The Ruler of Conspiracy Arc
As part of Ainz's persuasion to get Pluton Ainzach to trust him in turning the Adventurer's Guild from a mercenary group to real adventurers to explore the unknown and new lands. Ainz used the Aberion Hills as an example of what sort of potential exploring new lands would mean to the adventurers.

Ainz also spoke of providing support and assistance to all guild members if they would agree with his new reforms and is also seeking to use their help with finding more detailed information of the people that live there and what opportunities the land itself could provide.

Furthermore, Ainz mentioned that the Sorcerer Kingdom is making preparations for any potential future conquest, however only once that available information is procured and assured that he will not involve the Guild in their subjugation.

The Paladin of the Holy Kingdom Arc
and The Paladin of the Holy Kingdom II Arc At some unknown point in time, Demiurge, under his Jaldabaoth guise, conquered and enslaved about eighteen different demi-human races from the Abelion Hills in his conquest of the Holy Kingdom. He then forced all those who were combat-ready into a huge allied army and attacked one of the fortresses at the Holy Kingdom's Great Wall. After Jaldabaoth single-handedly destroyed the fortress along with a section of the wall, he ordered his army to finish off any surviving soldiers. Once that was done, the demi-human army marched through the opening in the wall into the Holy Kingdom.

After Jaldabaoth invaded the Holy Kingdom and conquered the North, he left one of his trusted demon subordinates and servitude of demi-humans under them to manage the territory while its other brethren attacked cities like Loyts.

When Ainz Ooal Gown supposedly was killed by Jaldabaoth, it was believed that he has fallen into the Abelion Hills. Fortunately, he miraculously survived the first deathmatch with Jaldabaoth, reappearing with his own demi-human army. He fought in his second and final standoff with the said Demon Emperor as the latter was about to destroy the Holy Kingdom Liberation Army. He said that he merely fell into the Abelion Hills region, where he has recuperated, and rallied the local demi-humans before coming back to overthrew the reigning demon. Whereafter he claimed the region for the Sorcerer Kingdom.

Layout
The area consists mostly of a patch of wilderness that consists of mostly hills and wild forests. Its borders make up of mountain ranges in the south, east which neighbors the Slane Theocracy and the north by the Re-Estize Kingdom and by the Great Wall of the Roble Holy Kingdom in the west.

Known Inhabitants
The Abelion Hills is home to various demi-human tribes that consists of numerous races. The known ones so far that invaded the Holy Kingdom with Jaldabaoth are the eighteen different species such as Snakeman, Armatt, Zern, Ape Beastman, Blader, Centaur, Caben, Horuner, Spidan, Stone Eater, Pteropos, Orthrous, Magelos, Bafolk. There are six other races that are not numerous, but very powerful such as Spriggan, Naga Raja, Vah Un, Ogre, Puri Un, and Zoastia. Additionally, there would be other species living the Aberion Hills such as Srush, Giant Biclop, Weremen, Pandex, Orc, Hill Giant, Goblin and Dark Dwarves. Among the demi-human tribes were individuals that are noted to be skilled and fearsome warriors.
 * Grand King of Destruction: Buser
 * Demon Claw: Vijar Rajandala
 * Black Steel: Muar Praxua
 * Rainbow Scales: Rokesh
 * Beast Emperor
 * Ashen King
 * Iceflame Lightning: Nasrene Belt Cure
 * Spiral Lance: Hectowaizes Ah Ragara
 * White Elder: Halisha Ankara

Trivia

 * Metal appears to be scarce in the area and is a commodity that the local tribes quarrel over. Dark Dwarves in this area traded metal-made goods in exchange for slaves.
 * There had even been cases where some of the demi-human tribes had been driven out of their land and forced to attack the Holy Kingdom.
 * In addition to Demi-Humans, some Heteromorphs have also made this place their homes like the Zern and the Pandex.