Yi Toi-Gye's leadership in this school of thought pulled him into the political arena. The Joseon Dynasty was characterized by political and religious reform with frequent conflicts between scholars and officials. As the underlying principle behind these changes, neo-Confucianism began to dominate the state creed and politics of the Joseon Dynasty. Under this pressure, all of the Korean Buddhist sects were forced to unify into one of two groups, Son (den) or Kyo. Because Buddhism was viewed by strict neo-Confucians as a social evil, all but 18 of the nation's main Buddhist temples were closed. Political differences ultimately became focused on neo-Confucian concepts and their differences rather than on political problems.
Although he died in 1570, Yi Toi-Gye, through his teachings, had great historical impact on Korea during the years that followed. A member of his school of thought, Kim Hyo-Won, occupied a post of considerable power, enabling him to hire, dismiss, or veto all government appointments. When the leader of the opposition party, Sim UP Gyom, arranged to have his brother succeed him, Kim exercised his veto power. This act polarized the entire government. Eventually every official had to become aligned with one side or the other or risk attack by both. Since Kim lived in the eastern quarter of Seoul and Sim lived in the western quarter, the two factions became known as the Easterners and the Westerners The Easterners followed the teachings of Yi Toi-Gye while the Westerners followed the teachings of Yi .
This feuding continued long after Kim and Sim had disappeared from public life and often took the guise of schemes designed to exile members of the rival faction, remove them from office, or get them executed on false charges. Their philosophical differences tended to drive the two factions further apart, increased the conflicts, and made the functioning of government virtually impossible. The day-today functioning of the government and military became so impotent that resistance to the Japanese invasions of Korea by Hideyoshi (200,000-man force) in 1592 and 1597, and the Manchu attacks in 1627 and 1637, were totally ineffective.
No doubt Toi-Gye would have been sorely dismayed had he lived to witness the political problems that beset Korea in the name of his teachings. Despite the role it played in that dark chapter of Korea's history, Toi-Gye's philosophy has made an enriching contribution to neo-Confucian thought. His influence is still being felt in the 20th century in China, Korea, and Japan. His academy remains a center for the study Toi-Gye thought, and regular memorial services are held in honor of its founder twice a year.