Many many eons ago the nine domains used to be one realm, perfect in every way.
The elements where balanced and all life lived in harmony.
Gods where doing they're godly duties protecting the harmonious balance, and mortals doing what mortals do best multiplying and giving life to the realm.
One day one God decided to do something that will forever leave the realm changed, he made mortals fear death making them realize how insignificant they are.
Fear ran the world for many millennials until one mortal had enough, since Gods get to live forever and never die why cant he do the same.
By a stroke of lucky or destiny he was enlighten and created the very first cultivation technique , it was crude and full of flaws but he had done it giving mortals hope for immortality.
Time passed and his technique refined and more come after by his predecessors, soon all races had their own version of the technique.
The Gods watched from high above amused by the so called technique that aim to steal their power.
Everything was all well and good until the founder of cultivation did the impossible again.
He used the power of gods he acquire from cultivation and killed a god.
It is not known how he did it but for the first time ever a mortal killed a god permanently.
His action sparked fear among the gods with the discovery that they can now die permanently.
Enraged by the ants that can now kill them gods waged war against mortals.
War raged the world for many years because of his action, a war where gods and mortals fight each other.
There came a time in the war when some gods and races became allies, fighting other aiming to be the last race and god of the realm.
The whole realm bathe in the blood of mortals and gods alike.
Some races went extinct and many lost their members in the war.
Curses and spells on unimaginable scale where cast, weapons of mass destruction were fired across the realm.
Eventually the realm could not handle the war and split in nine pieces.
Those pieces becoming the 9 domains of today.
The resentment of the war that lasted countless years became so thick that it liquified and sip between the domains in a form of rivers that continuously birth monsters upon the land.
One powerful god upon death cast a powerful curse that made it so mortals are unable to cultivate.
Once a door close it cannot be closed, it was later discovered that after the war since the god that managed the afears of death and the afterlife perished when a mortal dies their life force and their souls liquifies.
When mortals bathe in this essence they become powerful.
All around the 9 domains at places where the essence forms they built cities to protect themselves from the monsters formed from resentment.