Founding of Jin
Dae Joyeong ( 대조영 ), who later came to be known as King Go ( 고왕 ), was born in Goguryeo (although this is disputed by Chinese scholars who claim that he was born in Sumo Mohe) and served as a general before the fall of Goguryeo in 668. He was forced to relocate with his father, named Dae Jung-sang ( 대중상 ), to a Tang province after the fall of Goguryeo. However, his father took advantage of the chaos following a Khitan invasion in 696 to gather a group of followers, which consisted primarily of people from Goguryeo and Sumo Mohe (also known as the Malgal), and lead them to Dongmo Mountain ( 동모산 ). Tang took notice of this movement and sent an army to fight these men in the Battle of Cheonmunryeong ( 촌문령 전두 ). Dae Jung-sang and the leader of the Mohe people were both killed in the battle, but Dae Joyeong was able to successfully repel the attacks and later founded the state of Jin in 698 and named himself King.
King Go changed the name of his state to Balhae in 712 and attempted to expand the influence of his fledgling kingdom. King Go's son, King Mu, was responsible for the first significant expansion of the kingdom and as a result gained the contempt of both Tang and Silla. The ire of these two kingdoms was countered by forming diplomatic ties with Japan and tribes in northern China in order to deter any aggression by either of these powers. Balhae's third ruler, Emperor Mun ( 문왕 ), had the longest reign in Balhae's history and is credited with stabilizing and centralizing the rule of what he labeled as an empire. He is credited with establishing friendly contact with neighboring states (specifically Tang) and encouraging cultural exchange between kingdoms. He also moved the capital several times before his grandson, King Seong ( 성왕 ), permanently established its location at Sanggyeong in 793.
Height of Power
The kingship went through a period of instability after the death of Emperor Mun as 6 rulers took the throne over the next 25 years. However, Balhae would reach the apex of its territorial expansion when King Seon ( ) took the throne in 818. He successfully subjugated tribes in all directions, with end result being a kingdom that stretched from the Liaodong Peninsula between China and Manchuria all the way up through modern-day Russia. The authority of the throne was also increased during this time to successfully meet the demands of ruling over such a vast kingdom.
Decline and Fall
Unfortunately, I was unable to find any real information on the kings who ruled after King Seon. The only ruler with any significant amount information is Dae Inseon ( 대인선 ), who was the last king of Balhae. As a side note, all of the Balhae kings after King Seon do not use the term "wang", which means king, in their names. They instead simply use the family name Dae, which was the name of the royal family. But anyway, Dae Inseon ruled during a very turbulent time period in East Asia. The Korean peninsula was undergoing a transformation from Silla's dominance to the rise of Goryeo, while Tang was dealing with multiple peasant revolts. It is unknown what exactly caused the internal crumbling of Balhae, but two predominant theories exist. The first has traditionally been accepted by historians and suggests that a rift occurred between the Goguryeo and Mohe populations. A new theory has recently arisen to challenge this idea and suggests that instead a volcanic eruption was actually responsible for weakening the kingdom. The exact details of Balhae's deterioration are unknown, but is known that the Khitan (then known as the Liao Dynasty, which was located in northern China) invaded in 925 and succeeded in conquering Balhae the following year.
The Khitan established the Dongdan Kingdom in Balhae territory, but the Balhae people were unwilling to accept their new rulers. The Balhae citizens began rebelling against the Khitan almost immediately and a successor state named Later Balhae was established by the Dae royal house in 927. This revival movement eventually transformed in the Jeongan Kingdom ( 정안국 ) when Yeol Manhwa ( 열만화 ) took control in 935. The kingdom attempted to undermine the rule of the Khitan, but it was eventually defeated in 986.
Balhae developed a sophisticated system of government that was largely based upon the Tang Dynasty and contained three chancelleries and six ministries. The government positions were predominantly made up of people with Goguryeo ethnicity, which ultimately led to the rift that occurred between the Goguryeo and Mohe populations. Confucianism also played an important rule in the government structure, which is a marked difference from their Korean neighbors to the south. An interesting aspect of the structure outside the capital was the existence of four secondary capitals (which is believed to have been influenced by Goguryeo).
There were five classes in Balhae: the royal house, the aristocracy, the commoners, the lowborn, and the slaves. As stated previously, the royal house and the aristocracy consisted of people from Goguryeo, while the Mohe made up much of the remaining three social classes.
Balhae's economy consisted of many different facets, which is to be expected from such a large country. Agriculture (specifically dry crops), livestock, fishing, hunting and crafts all contributed to Balhae's economy. There is also some dispute over the use of a currency system in Balhae, but it seems likely that currency and barter were used interchangeably.
As was the case with Goguryeo, Balhae lived on land that was not well suited for agriculture and as a result the kingdom sought frequent trade with its neighbors. It is said that Balhae brought trade in East Asia to unprecedented levels.
Buddhism was actually not a dominant mode of thought in the early years of Balhae. It wasn't until the rule of Emperor Mun that Buddhism really started to become popular. It seems as though Buddhism became popular with all social classes and influenced much of the art in Balhae. Taoism also seems to have played an important role in Balhae, which was likely the result of influence from Goguryeo and Tang.
As was the case with the three kingdoms, the only extant paintings are found on the walls of tombs. The tomb of Princess Jeonghyo and the tombs at Sanlingtun provide the best examples of Balhae painting techniques.
Music in Balhae was more than likely a mix of the music from Goguryeo and Mohe. Japan has numerous records of Balhae music, the earliest of which dates to 740.
Glazing came into use during the time of the Balhae Kingdom.
The culture in Balhae was apparently so advanced that China referred to the kingdom as the "flourishing land in the East." However, the ultimate legacy of Balhae is as the last Korean state in Machuria. Goryeo took over the Korean peninsula shortly after the fall of Balhae and controlled almost all of modern-day Korea, but nothing more. From this point onward, Korean society would be constricted to the Korean peninsula.