The rebellion of Jeong Yeo-rip in 1589, known in Korean as the Gichuk oksa (기축옥사, 己丑獄事), was one of the bloodiest political purges in Korea's Joseon Dynasty.
During King Seonjo's reign, the Sarim scholars following the Kim Chong-jik's school of Neo-Confucianism seized power after long period of persecution and purges.
However, the younger generation, called Easterners because its leader Kim Hyo-won's house was on the east of the palace, regarded Shim and older Sarim officials as partly responsible for excesses of Myeongjong's reign, which was notorious for corruption and abuse by Yoon Won-hyeong, Myeong's maternal uncle.
After Yi I's death, however, the conflict between two factions became more intense as the Easterners impeached Shim Eui-gyeom, leading to his dismissal, and gained the upper hand.
As Easterners began to take key positions, Jeong Yeo-rip changed his affiliation from the Western to Eastern faction and criticized his teacher Yi I after his death, earning hatred and contempt of the Westerners as well as Seonjo, who greatly respected Yi I. Jeong left the court and went back to his hometown where he formed a private society with his supporters.
One day a government official in Hwanghae province reported to King Seonjo that there was conspiracy for rebellion in his areas and that their leader was Jeong Yeo-rip.
For a long time in Korean history, Jeong Yeo-rip's rebellion has been accepted as a fact even by the Easterners, but some historians note that there was no evidence except confessions from tortured followers and letters and writings discovered in his house, which could have been forged.
One of his sons was Song Yik-pil, who became a scholar of such renown that he formed friendship with Yi I and leading Westerners who praised that his achievement was enough to cover his father's crimes.
[3] It is remarkable indeed that Song Yik-pil overcame the fact that his father not only betrayed his master and benefactor, which would be considered one of the worst sins in Confucian world, but caused one of purges against the Sarim scholars, especially Jo Gwang-jo's supporters.
By Seonjo's reign, the Sarim faction took control of the government and Jo Gwang-jo and Ahn family were fully rehabilitated as their martyrs.
According to some accounts, it was while Song Yik-pil was in Hwanghae area that the accusation of treason was made against Jeong Yeo-rip, who lived in Honam.
Indeed, Yi Bal and his brother, Choe Young-gyeong (greatly respected scholar of Yeongnam School), and many others died in prison of torture or illness.
The Treason Case of 1589 is significant as the moment when the conflict within Sarim faction was irrevocably marred with bad blood, becoming a struggle of life and death that characterized many periods of Joseon politics.
The Eastern faction was further split between hardline Northerners and moderate Southerners over the question of punishing Jeong Cheol and other Westerners.
Some historians blame Treason Case of 1589 for the subsequent discrimination against Honam region as land of rebellion, whose effect is still felt today.