Yi Si-ae's Rebellion was an armed rebellion in 1467 in Hamgil Province (later renamed Hamgyong Province) led by General Yi Si-ae, a member of Yangban landowners in Kilju, Hamgil Province, to rebel against the centralized policy of King Sejo.
Background
Hamgil Province was the home province of King Yi Seong-Gye, the founder of the Joseon Dynasty. Taejo established this area as his base of power, subjugating the Jurchen tribes and increasing his strength. During Sejong's era, the river area expanded up to the Tuman River, and the people of Samnam-ni, Gangwon moved to make Hamgildo a province. However, in a situation where they always had to face off against the Jurchen raids, it was necessary to make enormous human and material sacrifices to defend Hamgildo, which put a tremendous burden on the people of Hamgildo. After the founding of the Joseon Dynasty, to effectively rule and protect Hamgildo and give preference to the birthplace of the royal family, the local nobles were appointed as local officials and led from generation to generation.
However, after King Sejo came to power, he strengthened the centralization policy to gradually reduce the number of officials from the north and dispatched officials from the south to govern the province. Sejo also passed the Hopae System to regulate the movement of Joseon's subjects further. The nobles in the northern regions feared that they would lose control of the commoners, causing dissatisfaction among the northerners. Yu Ja-gwang, who participated in the subjugation army at the time of Yi Si-ae's rebellion, understood that the reason the rebellion spread was that the officials dispatched to Hamgil-do were inexperienced with the region and abused the people. Moreover, officials sent from the central government harassed the people with projects such as fortifications. As a result of regional discrimination against Hamgil residents, the people protested against appointed officials from abroad and local councils (Hyangcheong, , ) in Hamgil unified their forces against the central government.
Prelude
Yi Si-ae first served as Heungjin's military commander in 1458, deputy commander in 1461, and magistrate of Hoeryong City in 1463. Initially, since the province had some exceptional circumstances of geographical proximity to Jurchens from the north, the court-appointed local officials from among the well-known nobles to rule the region from generation to generation. However, Sejo strengthened the centralized system and reduced northern officials, which made Yi feel uneasy about his position.
Yi Si-ae, his younger brother Yi Si-hab and son-in-law Yi Myeong-Hyo took advantage of the opportunity on leave for Hamgil Province due to his mother's death and rallied disgruntled nobles and residents of the northern provinces to organize and agitate the public while retiring from office. He stirred public sentiment by spreading rumors that soldiers from Pyeongan and Hwanghae would also cross Seolhanryeong Pass and enter Hamgil.
However, the officials and nobles criticized the rumors by Yi Si-ae as nonsense so that they would not be deceived and sympathize with the rebellion.
On May 10, 1467, he attacked and killed Kang Hyo-mun, the Hamgil-do provincial army commander (byeongmajeoldosa,兵馬節度使). At the same time, he killed Magestrate Seong Jeong-Shin of Kilju, Judge Park Soon-dal of Kilju County, and Kim Ik-su of Puryong County, which helped Yi Si-ae win the support of the people of the northern provinces, starting the rebellion.