Here is a good story so far timeline based off what I seen from a translated source with me putting in things from our version:
Far past ( Time Unknown )
There was the nation of Bulla (not enough information, mentioned only in certain legendary quest items)
Black Dragon Cult(?) is said to have existed since this time
Story from about 1000 years past
Twilight Edge(The sword we see Jin Seyeon carring about) is forged from a meteor that fell from the sky.
Sesin(the buddhist monk-like dudes) is formed
The Naryu Empire ruled the 4 continents with powerful machines, the Beopgis.
Chun Jin Gwon (In our version he's just called Mushin and his house is called the Mu) was despised by the court because he was born to a concubine with low blood status.
Only the Three Royal Elders(Later known as the Three Mushin Elders) protected and taught the him.
The Mushin Tower was built to train Mushin, whom after lengthy training and overcoming many difficulties earns the title Mushin(God of Martial Arts)
He later becomes a Great General of the Naryu Empire and unlike the royalty, many people follow Mushin as he was not only extremely powerful, but also had excellent virtue(?)
However the royal court considered this a threat and he was conspired against by his own brothers and was thrown in jail.
This unlocked the deep hatred within Mushin's heart that had been there since his childhood, and Mushin became untrusting and furious against humanity.
The Pain, Fury, and Darkness (not sure if correct) seen in the Tower of Mushin are the traces of these days.
It is about this time the heavens decide to choose 4 great beings to fight against the growing chaos and darkness.
These four were bestowed with amazing strength and were to live forever and to be stronger than any other mortal.
The four were
The Expert Swordsman, The Celestial Sword(Kum-sun) Biwol
The God of Martial Arts, Chun Jin-Gwon
The Master of Force and Magic, The Specter(Hwan-Gui) Ik San-Un
and the one said to have no equal in Brute Force, The Force King (Yuk-Wang) Hong Seuk-Geun.
These four became to be called the Four Great Guardians and were praised by the people.
They were called upon times of great peril.
Unlike the upright Bi-wol and Hong Seuk-Geun(Master Hong the teacher of the hongmoon arts), the talkative Ik San-Un favored Mushin because of his easier personality.
This however results in blindly trusting Mushin and starting a great tragedy later.
They were all forbidden from making any ties to the mortal world however they all break it at some point.
First was Mushin, for he left descendants.
With the help of the Three Mushin Elders, he creates the Tomb of Mushin to only allow the one
with his blood may enter and receive power. He also created the Silver and Gold Locks as the key to entering the tomb and left it with the Mu-Young Dan, the secret organization of the Naryu Empire. Finally, he teaches the Hwe-rangs (the wolf like guys) how to create the Mushin Compass which will react to the blood of Mushin.
Sometime later, a Naryu Royalty proceeds with the Chun-Myung Ceremony and brings forth the Demon King himself.
The Four Great Guardians fought against the demon and Mushin attempts to sacrifice himself to take down the Demon King using the Twilight Edge.
Although successful in banishing the Demon King while surviving, Mushin is consumed in the darkness fueling the already existing hate in his heart.
As time passes he sees humanity as it is and the hatred towards it grows to the point where he decideds to become partners with the underworld and to become to ruler of the human world.
At this point the Demon Yura goes undercover in the human world in an attempt to bring the demon king back.
Also the fight against the underworld continued all around the world with Mushin excusing himself to fight back the darkness from his attempted sacrifice, of course he was only taking this time to master the darkness to make it his own.
The fight resulted in turning the Northern Lands, which was originally full of green into an ever-snowing whitelands and burned and dried to Naryu capital to create the great Desert.
The Chun-Bloodline and the Naryu empire falls and in its place is created the Un-Empire of the Seop-Bloodline. They base the capital in an area west of the great desert, the KeonwonsungDo, (Recently updated in KR server) and goes on to rule most of what was previously ruled by the Naryu.
The Muyong Dan, secret Naryu Organization, was supposedly destroyed at this point, but a small faction manages to survive.
30-50 years past
Baek-Mugi comes to Biwol in wishes of learning her Sword but Biwol refuses because she wasn’t supposed to create ties. However Baek-Mugi builds a hut beneath the Biwol Peak and constantly seeks the help of Biwol. She ends up giving some pointers. People started gathering and was created the Baekchung Pa, one of the greatest Sword Styles in all of the continents. (This is essentially similar to the blade master style we have today in game)
30 years past
Seop Hwan, the youngest prince becomes emperor of the The Stratus Empire . The Eldest Seop Mu becomes the lord of the western continent and the second Seop Gwang becomes the lord of the eastern continent. However at the time the Western and the Eastern continents were mere colonies to the main provinces in the South, so they were less than happy.
The Eldest performs the Chun-Myung Ceremony, believing that it will bestow him the right to be empire. He fails, however, the western continent is swallowed entirely in darkness and no living thing could survive on the continent. It was thereafter called SeoRak(I’m guessing Evil of the West) and not even the daring Black Ram pirates dared to sail in its direction. The few survivors fled to different continents. Jin Seyoen was a mere child when she escaped the continent.
The Darkness from the west began growing into the Northern continent and the Un Empire began to shake after losing two continents. In this time of need, the youngest price, and now Emperor Seop Hwan is wasting the nation’s money on drinking and women.
The Second prince, Seop Gwang was not much different for he was drinking is life away in agony that he wasn’t made emperor. He calls upon the demon Yura, who was disguising herself as a Ki-Nyeo(Something like a Geisha) and falls in love with her. Yuran convinces Seop Gwang to perform the Chun-Myung Ceremony to become Emperor himself but only ends up destroying the Old City. (As seen in-game).
Nam-Sullin is chosen to become a concubine, however she was in a relationship with the country’s general Kun Ma-Yum.
Kun Ma-Yum is sent to the eastern continent to fight the rebellion that broke out. Kun Ma-Yum succeeds and becomes the hero of the Empire.
At this point Nam Sullin bears the daughter of the Emperor and names her Seop Soyu. She goes to Un-Rim Temple in the Eastern continent to take a break. There she meets with her true love the Great General and the Hero Kun-Ma-Yum.
However there was an attempted assassination of Nam Sullin and Soyu by the Queen Ak, who felt threatened. The assassination was unsuccessful(as seen in-game), however the queen reveals that Nam Sullin and Kun Ma Yum are actually lovers and creates a rumor that the two were conspiring against the empire.
Also, the assassin who was about to kill the baby is the same person as the monk Hyun-dam.
After one of his greatest lieutenants Geo-Geo Boong (The huge dude that hangs around with JSY) was executed for treason Kun Ma Yum realizes that everything he loves is at stake and starts a rebellion in the east. He kills all Un soldiers that refused to follow him and creates a new nation called the Talus Dominion .
Naturally war broke out between the two countries, and at first the Talus Dominion Poong was losing drastically and almost lost it capital Kang-Ryu. However the tides changed as JSY joins the Talus Dominion .
With her excellent tactics and brute force she begins forcing the Un forces back. The remaining forces that couldn’t make it all the way back resided in the Suwol provinces and began retaliating against the Poong in small resistances that end up becoming the KyungChun Maeng.
After the war, despite the history and the opposition of the council, the Emperor of the Poong, Kun Ma-Yum takes his lover Nam Sullin as queen and promotes JSY as high councilor for her efforts in the war.
10’ish years past.
Kun Ma-Hye is born as a princess however Nam-Sullin dies in childbirth.
Kun Ma-Yum, in his grief, loses interest in politics and the reigns are, in reality, handed over to JSY. With Yura now working with JSY, they prepare for the next Chun-Myung Ceremony to bring back the Demon King.
And that starts where we are today. The story gets a bit more deep than that but if I elaborate more some things will be spoiled.
Credit to Unexpired at Blade and soul dojo for the translation