They primarily served in so-called Three Offices, from which challenged the entrenched "Hungu" officials, who accumulated great power and wealth by supporting King Sejo when he usurped the throne from his nephew.
They enjoyed a brief period of power during Jungjong's reign through Kim Gueng-pil's disciple Jo Gwang-jo, who pursued radical reforms to transform Joseon into an idealistic neo-Confucian society.
After four major purges that saw Jo Gwang-jo and many others executed, the Sarim scholars again retreated to rural villages where they continued to spread their philosophy through local schools called seowon and maintained their power base through the system of Hyang'yak.
For instance, the Eastern faction was largely Yeongnam-based, and its subfaction Southerners were mainly followers of Yi Hwang while Northerners coalesced around the school of Jo Shik.
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.
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.
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.
According to Westerners' accounts, Jeong Cheol tried heroically to save Yi Bal and Choe Yeong-gyeong from Seonjo's wrath.
In an Easterner plot to make it seem the Westerners were attempting to murder Prince Sinseong, Jeong Cheol was exiled in 1591.
The Southerners, led by Yu Sŏngnyong, 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.
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.
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.
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.
Under the reigns of Yeongjo and Jeongjo in the 18th century, the kings pursued a strict policy of equality, favoring no faction over another.
The division and subsequent conflicts of these factions generally revolved around minor issues and reflected dogmatic and the rigid nature of their philosophical interpretations.
For most of the 19th century, the Jangdong branch of the Andong Kim clan was in control of the government, which led to rampant corruption throughout the country.