In the late 800s, Unified Silla weakened as rebellions and local warlords expanded their control. Rival states emerged, creating the “Later Three Kingdoms” period. This instability set the stage for Wang Geon (later King Taejo) to build a new coalition and pursue unification.
Kung Ye established a northern rival state (often called Taebong) as the peninsula fractured into competing regimes. Wang Geon rose within this state as a leading commander and political figure. Taebong later became the base from which Wang Geon seized power and founded Goryeo.
Early in his reign, Taejo promoted settlement and defense in the Pyongyang area, reflecting his focus on northern security. This policy supported border stability and reinforced claims to territories linked to earlier northern states. It also shows that unification planning included both internal rivals and frontier defense.
Senior generals overthrew Kung Ye and installed Wang Geon as the new ruler. This coup removed an increasingly unpopular leader and shifted power to a coalition that backed Wang Geon. The takeover directly enabled the creation of a new dynasty.
After taking power, Wang Geon renamed the state “Goryeo,” presenting it as a successor to earlier northern kingdoms and as a new center of authority. This marked the formal start of the Goryeo dynasty. From this point, unification became a central goal of Taejo’s rule.
Taejo shifted the capital to Gaegyeong (near modern Kaesong), strengthening control over key elites and trade routes. Establishing the capital there helped stabilize the new regime after the 918 coup. It also positioned Goryeo to project power across the peninsula.
Later Baekje forces attacked Silla’s capital, killing King Gyeongae and installing Gyeongsun as a dependent ruler. The assault demonstrated Silla’s inability to defend itself and accelerated its collapse. It also triggered Goryeo’s urgent need to counter Later Baekje militarily.
Taejo attempted to strike Later Baekje forces near Gongsan but suffered a severe defeat, losing many troops and key generals. The loss showed that Goryeo’s unification effort was not inevitable and required rebuilding. Goryeo’s ability to recover from this setback became a turning point in the long campaign.
Goryeo defeated Later Baekje forces at Gochang (in the Andong area), strengthening its position after the earlier defeat at Gongsan. This victory helped Goryeo expand influence in strategic central regions. It contributed to a broader momentum shift toward Taejo’s eventual unification.
King Gyeongsun, the last ruler of Silla, surrendered his kingdom to Taejo, ending Silla as an independent state. Taejo incorporated Silla elites into the new order, reducing resistance and supporting a peaceful transition in the southeast. With Silla absorbed, the unification struggle narrowed mainly to Later Baekje.
In Later Baekje, Kyŏn Hwŏn was overthrown by his son Kyŏn Sin-gŏm and imprisoned, but escaped and fled to Goryeo. Taejo welcomed him, turning a former rival into an ally and gaining valuable military and political support. This internal split badly weakened Later Baekje right before the final campaign.
Taejo and his forces defeated Later Baekje in a decisive battle at Seonsan (also associated with the final collapse of the Later Baekje regime). After the defeat, Later Baekje surrendered and its leadership was absorbed or exiled. This victory ended the Later Three Kingdoms conflict and completed Taejo’s unification of the peninsula under Goryeo.
Near the end of his reign, Taejo was remembered as leaving the “Ten Injunctions” (Hunyo sipjo), advice for his successors about ruling and maintaining stability. The text became part of later historical tradition and is discussed by scholars, including debates about its exact origin and date. As a legacy document, it reflects how early Goryeo leaders framed the challenges of governing a newly unified kingdom.
Wang Geon and the Founding of Goryeo: Unification Campaign (918–936)