[Lee Sang-hoon's Korean History] The Largest Civil War of Unified Silla: 'Kim Heon-chang's Rebellion'

Rebellion Citing Father’s Failed Ascension to Throne
Kim Heonchang Who Seized Half of Silla Territory
Cut Off Supply Lines, Failed, and Committed Suicide

Sanghoon Lee, Professor of Military Science at the Korea Military Academy

The cause of the rebellion was that his father, Kim Juwon (金周元), did not ascend to the throne. When King Seondeok died without a son in 785, several officials tried to enthrone Kim Juwon, who was the king’s nephew. At that time, heavy rain caused the water level of Alcheon (閼川) to rise, and Kim Juwon could not arrive at the royal palace on time. Taking advantage of this, Kim Gyeongsin (金敬信) ascended the throne as King Wonseong. This account contains many legendary elements. However, it is clear that Kim Gyeongsin’s faction excluded Kim Juwon’s faction and seized the royal authority. After ascending the throne, King Wonseong granted Kim Juwon the territory of Myeongju (Gangneung) as a fief and forced him to retire from the central government.

Kim Heonchang used the fact that his father Kim Juwon did not ascend the throne as the justification for his rebellion. However, the issue of Kim Juwon’s succession was a matter from over 30 years earlier. Myeongju, where Kim Juwon had settled, did not join Kim Heonchang’s rebellion. The faction of Kim Jonggi, Kim Heonchang’s elder brother, also did not participate in the rebellion. Considering the nationwide scale of the rebellion, the direct cause must be sought elsewhere.

At that time, there was resistance in Silla society surrounding political reforms by King Heondeok and his brothers Sujong (秀宗) and Chunggong (忠恭). Kim Heonchang himself was appointed as a local governor (都督), which caused dissatisfaction with personnel policies. Especially, when King Heondeok’s brother Sujong was appointed as a deputy lord (副君), Kim Heonchang’s rank in the royal succession was further diminished. Besides these personal grievances, the unsettled sentiments of the local populace also seem to have played a significant role in the rebellion.

Kim Heonchang’s Dissatisfaction with Personnel Policies
Rebellion Triggered by Being Pushed Down the Succession Line
Controlled 5 Provinces and 3 Small Districts out of 9 Provinces and 5 Small Districts

Kim Heonchang controlled 5 provinces and 3 small districts out of the 9 provinces and 5 small districts. The regions that joined the rebellion were Ungcheonju, Wansanju (Jeonju), Mujinju (Gwangju), Sabeolju (Sangju), Cheongju (Jinju), Gukwon Small District (Chungju), Seowon Small District (Cheongju), and Geumgwan Small District (Gimhae). Kim Heonchang’s power base covered half of Silla’s territory, centered on the former Baekje region. As a result, Silla was cut off from the northern provinces of Hansanju, Uduju, and Myeongju, and the areas around Gyeongju were completely surrounded by rebel forces.

King Heondeok quickly organized a suppression army. First, he selected eight generals and stationed them at eight locations around the capital. He assigned the Sangdaedeung Chunggong to defend the cultural gate (蚊火關門) south of Gyeongju. Next, the attacking forces were divided into an advance unit, main unit, and special unit. The advance unit was led by Jang Ung, Wi Gong, and Je Neung; the main unit by Gyun Jeong, Ung Won, and Woo Jing; and the special unit was a Hwarang unit led by Myeong Gi and An Rak.

The advance unit attacked from Dodonghyeon (Yeongcheon) to Samnyeonsanseong (Boeun) and then headed to Ungjinseong (Gongju). The main unit passed through Dalgubeol (Daegu), fought at Seongsan (Seongju), and then moved toward Ungjinseong. The special unit advanced toward Hwangsan (Yangsan) in the lower Nakdong River area. From Gyeongju’s perspective, the advance unit first moved northwest to attack Samnyeonsanseong in Boeun, while the main unit moved west to fight the rebels at Seongsan. The special unit moved south to monitor the rebels’ movements.

King Heondeok became aware of Kim Heonchang’s rebellion and began organizing the suppression army on March 18. The rebellion was suppressed before April 13. The Silla army’s operation period was at most 25 days, less than a month. The siege of Ungjinseong lasted 10 days. Excluding this period, the army suppressed the rebels in the Gyeongsang and Boeun regions within about fifteen days and then entered Ungjinseong.

The straight-line distance from Gyeongju to Gongju is 200 km. Considering the transportation routes at the time, it was at least 250 km. If the Silla army covered 250 km in 15 days, they marched about 16 to 17 km per day. The average marching speed in ancient times was 12 to 24 km per day. This indicates that the Silla army marched somewhat quickly. Moreover, considering that they fought the rebels directly at Dodonghyeon, Samnyeonsanseong, Songnisan, and Seongsan during the march, the Silla army’s marching speed was quite fast.

Suppression Army Captures Samnyeonsanseong in Boeun
Rebels’ Strength Broken by Cut-off Routes
Final Resistance at Ungjinseong Lasted 10 Days

Let us reconstruct the process of the Silla army suppressing the rebels. The advance unit, which departed first, arrived in the Yeongcheon area and guided the main unit’s advance. Then, the advance unit fought the rebels at Samnyeonsanseong and Songnisan, while the main unit fought at Seongju. The two units separated at Yeongcheon and marched independently. The advance unit moved northward secretly toward Sabeolju, while the main unit moved westward toward Dalgubeol (Daegu), drawing the rebels’ attention.

If the main Silla army passed through Daegu and entered the Seongju area, the rebel forces in Sabeolju and Cheongju would be split north and south. When the main unit stationed in Daegu, the rebel forces in Sabeolju and Cheongju gathered in Seongju to avoid being defeated separately. Records show that the Silla army attacked first. Therefore, the rebel forces gathered in Seongju did not seem to overwhelm the Silla army. Since the Silla army was divided into the advance and main units, it would have been difficult to attack the rebels easily.

While the main forces of the Silla and rebel armies faced off in Daegu and Seongju, the Silla advance unit quickly moved north from Yeongcheon. They passed Sangju and launched a surprise attack on Boeun. The Boeun area, where Samnyeonsanseong is located, was a strategic point connecting Ungcheonju and Sabeolju. The Silla advance unit cut off the rebels’ main communication and supply routes. News of the Silla army’s capture of Samnyeonsanseong reached the rebels in Seongju. The tide began to turn. The Silla main unit attacked and defeated the wavering rebels, then proceeded directly to Ungjinseong.

When the Silla main unit entered Ungcheonju, the advance unit joined them to besiege Ungjinseong. The rebels inside Ungjinseong could no longer expect external reinforcements. Their morale inevitably plummeted. As the tide turned in favor of the Silla army, some factions sympathetic to Kim Heonchang likely defected to the Silla side. Eventually, the rebels were besieged in Ungjinseong for 10 days and gradually collapsed.

When the fortress faced imminent fall, Kim Heonchang judged that escape was impossible and took his own life. His retainers cut off his head and buried it separately from his body. After the fortress fell, the Silla army found Kim Heonchang’s head and body, reassembled them, and executed a posthumous humiliation (剖棺斬屍). They also executed 239 key figures who followed Kim Heonchang and released the remaining civilians.

Some argue that the rebel forces, mainly local militias, were easily suppressed. However, considering that Kim Heonchang ordered his generals to defend strategic points, that the rebel reconnaissance unit reached Dodonghyeon, and that the forces of Sabeolju and Cheongju gathered at Seongsan, the rebel command and control system was functioning properly. The defeat of Kim Heonchang’s formidable rebel forces was due more to the swift response of the suppression army than to any weakness of the rebels.

Weakening Royal Authority and Growth of Local Nobles
A Turning Point Leading to the Later Three Kingdoms Period

Kim Heonchang’s rebellion was suppressed faster than expected. However, Silla was rotting internally. Three years later, in 825, Kim Heonchang’s son Kim Beommum (金梵文) staged another rebellion in Bukhan Mountain Province, showing the significant aftereffects. Kim Heonchang’s rebellion greatly accelerated the local nobles’ tendency toward regional autonomy and intensified the struggle for royal succession. In this process, the aristocrats mainly mobilized ‘private armies’.

Kim Heonchang’s rebellion was the greatest civil war in Unified Silla. It marked the moment when the centripetal force of the Silla dynasty turned into a centrifugal force. While fierce struggles for the throne weakened royal authority, local nobles gradually grew stronger. In this process, the Silla regular army lost its function and became ineffective.

The Silla army, which had been the driving force behind the unification of the Three Kingdoms, completely collapsed during the late period. The regular army, one pillar supporting royal authority, was eliminated, and private armies prevailed. Ultimately, Unified Silla entered the era of division known as the Later Three Kingdoms period.

Professor Sang-Hoon Lee, Department of Military History, Korea Military Academy