Easterners vs Westerners

In the initial split of Sarim into the Western and Eastern factions, there was a large element of generational conflict. The Westerners were largely older Sarim scholars who had entered politics during Myeongjong's (1545–1567) reign while the Easterners, led by Kim Hyo-won (김효원) were mainly a younger generation who had become officials in Seonjo's reign and saw themselves uncorrupted by excesses of Myeongjong's era, which was marred by his maternal uncle Yoon Won-hyeong's corruption.

The Westerners were led by Shim Eui-gyeom (심의겸), Myeongjong's brother-in-law whose house was on the west of the palace. Although Sarim scholars were usually hostile to royal in-laws as a corrupting influence, Shim was Yi Hwang's disciple and protected Sarim scholars by impeaching his uncle who was planning another literati purge. In addition, many Westerners were disciples of Yi I and Seong Hon and followers of Giho school while many Easterners were disciples of Yi Hwang and Jo Shik and followers of Youngnam School. Easterners emphasized moral purification of the ruling class and rooting out corruption of earlier period while Westerners emphasized reforms that would strengthen the country and improve livelihood. (Easterners blamed Shim Eui-gyeom's ill-willed opposition to Kim Hyo-won's appointment at a key position in Ministry of Personnel for split while Westerners blamed Easterner's self-righteous attack.) Yi I attempted to prevent the factional split by appointing Shim Eui-gyeom and Kim Hyo-won to provincial posts far away from the court and arranging truce between Easterner Yi Bal and Westerner Jeong Cheol. After Yi I's death, however, the conflict between two factions became more intense as the Easterners impeached Shim Eui-gyeom and Jeong Cheol, leading to their dismissal, and gained upper hand.

In 1589, Easterner Jeong Yeo-rip was accused of treason because he had formed a society with his supporters that met each month to study and receive military training. The history of the Sarim after its split is very complicated because there is a wealth of conflicting historical accounts written by each faction. This is especially true with what became known as Gichuk Treason Case of 1589 (기축옥사), the bloodiest purge in Joseon history by far. There is still a dispute about the nature and purpose of Jeong Yeo-rip's group of armed supporters and whether it was treason or frame up. His group was not a secret society as it helped the local government in the fight against the Japanese marauders. On the other hand, it appears that Jeong truly had revolutionary ideas that were close to republicanism. He believed that the world was something to be shared and therefore could not have one master. His group, called "Great Common Society"(대동계), could be joined by anyone regardless of his social status, and it spread throughout Honam province and to other regions as well. Jeong Yeo-rip committed suicide after his arrest was ordered, which was considered the admission of guilt, and letters of Easterners were discovered in his house.

Jeong Cheol, famous poet and head of the Western faction, was in charge of investigating the case and used the case to effect widespread purge of Easterners who had slightest connection with Jeong Yeo-rip. According to Easterners' accounts, Jeong Cheol tortured even 80-year-old mother and 8-year-old son of Yi Bal, leader of Eastern faction. According to Westerners' accounts, Jeong Cheol tried heroically to save Yi Bal and Choe Yeong-gyeong from Seonjo's wrath. In any event, 1,000 Easterners were killed or exiled in the aftermath. It is also believed that Seonjo used this incident to weaken the Sarim's power.

Northerners vs. Southerners

This incident put the Westerners in power, but did not last long because of intrigue involving the appointment of the crown prince, which put the Easterners back in power for thirty years. The Eastern faction soon split into hardline Northern faction (Buk-in), which wanted to put Jeong Cheol and other Westerners to death, and moderate Southern faction (Nam-in), which did not want a wholesale purge.^[1] The Northerners were largely disciples of Jo Shik and Seo Gyeong-deok and suffered more from Jeong Yeo-rip's "rebellion" while the Southerners were largely Yi Hwang's disciples and less affected.

The Southerners, led by Yu Seong-ryong, were initially in power after Japanese Invasion in 1592, and maintained the policy of coexistence with Northerners and Westerners until its effort to reach peace agreement with Japan failed. The Northerners, now in power, split again over the proper successor to Seonjo, who had no legitimate son. Greater Northern faction supported Gwanghaegun while Lesser Northern faction supported another prince. During Gwanghaegun's reign, Greater Northern faction split further and persecuted other factions until Southerners and Westerners joined their forces in a coup d'état that deposed Gwanghaegun and placed Injo on the throne.

With the Westerners back in power, Joseon politics entered more stable stage in which they competed with Southerners in relatively peaceful coexistence for about 100 years. But under Hyojong's reign, the Western faction was becoming more powerful.

Sukjong's reign

In the early years of Sukjong's (1674–1720) reign, the Southern faction and Western faction clashed over the Royal Funeral Dispute, a seemingly minor issue regarding the mourning period for Queen Insun. The Southern faction claimed that the mourning period should last one year while the Western faction argued for a nine-month mourning period. A one-year mourning period meant that Hyojong was considered the eldest son while a 9-month period would suggest that Hyojong was considered not the eldest son, following the rules that governed the yangban class. In other words, the Western faction viewed the royal family as the first of the yangban class rather than a separate class for which different rules applied.

The two factions were also in conflict over the issue on fighting the Qing Dynasty, which was considered a barbarian government (as opposed to Ming Dynasty) that threatened Joseon's national security. The Southern faction, led by Huh Jeok and Yoon Hyu, supported war against the Qing while the Western faction wanted to focus first on improving domestic conditions. Under Sukjong's reign the factional fight became more intense and deadly since Sukjong frequently replaced factions in power with another one to strengthen the royal authority. With each change of government, which was called hwanguk (환국 換局), literally turn of the state, the losing faction was completely driven out of politics with executions and exiles.

Westerners vs. Southerners

Sukjong at first sided with the Southern faction, but in 1680, Huh Jeok was accused of treason by Western faction, which led to execution of Huh Jeok and Yoon Hyu and purge of Southern faction. This incident is called Kyungshin hwanguk (경신환국). Now in power, Western faction split into Noron (Old Doctrine) faction, led by Song Siyeol, and Soron (New Doctrine) faction, led by Yoon Jeung. After nine years in power, Noron collapsed when Sukjong deposed Queen Inhyeon, who was supported by Western faction, and named Consort Hee of Jang clan (or Consort Jang) as the new queen. Western faction angered Sukjong when it opposed the naming of Consort Jang's son as crown prince. Southern faction, who supported Consort Jang and her son, regained power and drove out Western faction, executing Song Siyeol in revenge. This is called Gisa hwangguk (기사환국).

Five years later in 1694, Southern faction was planning another purge of Western faction, accusing them of conspiracy to reinstate deposed Queen Inhyeon, when Sukjong began to regret deposing Queen Inhyeon and favor Consort Suk of Choi clan (Consort Choi), an ally of Queen Inhyeon and Noron faction. Angry with Southern faction's attempt to purge Westerners, Sukjong abruptly turned around to purge Southerners and brought the Western faction back in power. The Southern faction would never recover from this blow, also called Gapsul hwanguk (갑술환국). Sukjong demoted Queen Jang to Consort Jang and reinstated Queen Inhyeon. Consort Jang was eventually executed (with poison) for cursing Queen Inhyeon after the latter died. Soron faction supported the crown prince, Consort Jang's son, while Noron faction supported Consort Choi's son, Yeonying-gun (later to become Yeongjo). Late Queen Inhyeon and newly installed Queen Inwon were childless.

Soron vs. Noron

In 1718, Sukjong let the crown prince, soon to be Gyeongjong, rule the country as regent. He died in 1720 supposedly after telling Yi Yi-myoung to name Yeonying-gun as Kyungjong's heir, but in the absence of a historiographer or recorder. This would lead to yet another purge which led to the execution of four Noron leaders in 1721, followed by another purge with executions of eight Noron followers in 1722.

Under the reigns of Yeongjo and Jeongjo in the 18th century, the kings pursued a strict policy of equality, favoring no faction over another.^[2] However, in Jeongjo's reign, strife re-emerged as the ruling Noron faction split further between the Byeokpa and Sipa, two groups which cut across the earlier factions and differed in their attitudes concerning Yeongjo's murder of his son, who was also Jeongjo's father.