Balhae (also known as Bohai/Parhae) formed in 698 in the power vacuum after Goguryeo fell and as Tang influence expanded in the region. From the start, defense needs were shaped by a mixed population and borderland geography across Manchuria and northern Korea. Building a workable military system was essential to controlling territory and negotiating with larger neighbors.
Balhae organized its territory using a Tang-influenced administrative model: multiple capitals for regional management, provinces, and prefectures. This mattered militarily because local administration could support recruitment, supplies, and rapid response at distant frontiers. The same framework helped integrate different regions and peoples into a single defense system.
In 732, Balhae carried out a notable naval assault on Dengzhou on China’s Shandong Peninsula, reportedly killing the local prefect. The raid shows Balhae’s ability to project force beyond its land borders and highlights that maritime routes were part of frontier security. It also triggered heightened Tang concern about Balhae’s military reach.
After the Dengzhou attack, Tang and its ally Silla attempted a joint operation against Balhae, but the campaign was disrupted by harsh winter conditions and did not succeed. The episode illustrates how climate and terrain shaped frontier warfare in northeast Asia. It also encouraged Balhae to keep investing in defensive depth rather than relying on a single border line.
Balhae developed a capital-centered defense force organized into ten guard units (wi/衛), recorded in later Tang histories. These guards protected the royal palace and capital and helped supervise broader military resources. The system resembled Tang imperial guard models, showing how Balhae adapted large-empire practices for its own security needs.
Balhae made Sanggyeong (Shangjing Longquanfu) its capital from 756–785, and again from 793 until Balhae’s fall in 926. As a walled capital and political center, it anchored the kingdom’s command structure and concentrated elite guard units and administration. A strong capital core allowed Balhae to coordinate long-distance frontier defense across a wide realm.
Beyond the capital guards, Balhae relied on local forces tied to provincial administration. Local officials commanded militias that could protect settlements, roads, and key passes while also supporting larger mobilizations. This layered approach—central guards plus provincial forces—helped the state defend multiple frontiers at once.
Balhae stationed separate troops at important border locations, in addition to provincial militias. These detachments functioned as early-warning and rapid-response forces, strengthening control over contested edges of the kingdom. The result was a more flexible defense system suited to threats that could come from several directions.
Balhae returned its capital to Sanggyeong in 793, beginning the city’s final and longest period as the political and military center. Keeping a stable capital supported consistent planning for supply, recruitment, and coordination among the guard units and provincial commands. This stability mattered as regional power dynamics shifted after the Tang weakened.
In Balhae’s last decades, the kingdom faced increasing pressure from emerging regional powers, especially the Khitan. The last king, Dae Inseon (r. 906–926), is described as concentrating on strengthening defense capability in response to these threats. This period reflects how frontier defense priorities can intensify quickly when the balance of power changes.
In 926, Khitan forces captured Balhae’s capital and defeated the state, ending its independent military organization. The fall shows the limits of Balhae’s layered defenses when facing a powerful, expanding steppe empire with sustained campaign capacity. After this point, Balhae’s former territories were reorganized under new rulers.
Following Balhae’s defeat, the Liao dynasty set up Dongdan as a puppet kingdom to govern the conquered region. This change marks a clear endpoint: Balhae’s own military institutions and frontier defense decisions no longer directed the borderlands. Control of forts, garrisons, and administration shifted into the Liao state system.
Military Organization and Frontier Defense in Balhae (8th–10th centuries)