Battle of Tsushima Island
Part of the Mongol invasions of Japan
Date 2-4 November, 1274 Location Tsushima Island, present-day Japan Result Yuan victory
Belligerents
Yuan dynasty	Kamakura shogunate
Commanders and leaders
Unknown	Sō Sukekuni †[1]
Strength
8.000 And 900 Ships[1]	80
Casualties and losses
Unknown	Unknown

Historical records from the reign of Emperor Suiko provide evidence of Japan's interactions with the Korean Peninsula. According to these annals, along with various legends and traditions, the Japanese people emerged from a fusion of multiple groups from the northern continent and the southern archipelagoes. By the beginning of recorded history, Japan was an independent nation, largely insulated from the continental conflicts affecting China, Korea, and neighboring regions. The primary responsibilities of the Japanese emperors included subjugating local tribes that resisted central authority and defending the western islands, such as Iki, Tsushima, and the northern part of Kyushu, against potential invasions from the continent.^[2]

For fifty years, Japan frequently attempted to re-establish its influence over the Korean peninsula. During the reign of Empress Suiko (593–628), expeditionary forces were often sent to attack Sinra, but no significant restoration of Japanese prestige was achieved. Nonetheless, it was during her reign that relations with China were newly opened. Although Japan had lost direct control over the Korean kingdoms, its independence remained secure. Strong sea defenses ensured that neighboring states continued to respect Japanese authority, offering homage and tribute. In the reign of Emperor Kōtoku (645–654), a Pek-che envoy was rejected by Japanese authorities for presenting insufficient tribute. The Korean peninsula functioned as a strategic crossroads in East Asia, with kingdoms vying for dominance. While Japan had withdrawn from active involvement, China engaged with these states during its Tang period (618–907). In the reign of Emperor Tenchi (661–671), Sinra allied with China, creating a precarious situation on the peninsula. Koryo and Pek-che sought Japan’s assistance. Emperor Tenchi raised an expeditionary force to support these states, but the campaign failed, and China absorbed Koryo into its dominion. Given China’s longstanding position as the center of Eastern civilization and its strong foundations, Japan avoided direct conflict unless its own security was threatened. Japanese policy toward continental affairs emphasized caution, focusing primarily on protecting its own territory. To safeguard against potential invasions, Emperor Tenchi constructed a castle in Nagato and two in Tsukushi, strategically located on the northern coast of Kyushu. From these positions, defenders could monitor the Genkai Sea for approaching enemy ships. The islands of Iki and Tsushima, situated between the Korean peninsula and Kyushu, were also key points in the defense network.^[3]

Emperor Saga of Japan (810–824) appointed a Sinra language interpreter to the Tsushima Island in 814 and a learned official in 823, likely because the islanders frequently interacted with visitors from Sinra and were unfamiliar with their language and customs. Emperor Ninmei (836–850) organized garrisons in fourteen locations on Iki Island in 836 and another at Tsukushi in 844. Although Japan had long planned an expedition against Sinra, operations were delayed due to domestic campaigns against bandits in the northern districts. During this period, Sinra grew increasingly defiant, ceasing tribute payments and reportedly planning an invasion. In 867, the Japanese court received reports of Sinra’s attempted seizure of Tsushima. From 861 onwards, warnings circulated that "Sinra is coming." In response, Japan fortified its defenses: armor was supplied to Iki, distinguished knights and an archery band were stationed on Tsushima, and military forces along the northwestern coast were mobilized. Naturalized Sinra residents were relocated to eastern provinces to prevent espionage. Fujiwara no Fuyutsugu, head of the Dazaifu government, established coastal signal towers and prohibited horse exports from Buzen Province and Chikuzen Province. An officer plotting to betray Japan was arrested before he could communicate with the enemy. Following advice from Ariwara no Yukihira, a governor was appointed to an island called "Chika" (likely the Hirato Islands) off the Hizen Province coast, tasked with defending the straits.^[4]

According to Japanese tradition, a mysterious event was said to have occurred shortly before the first Mongol invasion of Japan reached Tsushima Island in October 1274. The island was home to a shrine dedicated to Hachiman, revered as the divine protector of Japan and the deity of war. On the morning of October 5, a fire reportedly broke out at the remote Hachiman shrine, even though it stood uninhabited among the island’s woods. The blaze was quickly extinguished, but the cause was unknown.^[5] Local accounts claim that a flock of white pigeons — considered sacred messengers of Hachiman — had flown from the north and landed on the shrine’s roof moments before the fire began. The island’s governor, Sō Sukekuni, interpreted this as a divine warning of imminent danger and immediately placed the island under martial law, mobilizing his garrison and posting sentries along the coast.^[6] Shortly thereafter, a large Mongol fleet appeared on the northern horizon. Historical sources describe this force as numbering around 900 ships carrying a combined army of Mongol, Chinese, and Korean troops. The fleet anchored in Sasu Bay (佐須浦, Sasu-no-Ura), preparing for an assault on Tsushima.^[7] A similar story involving the use of fire-bearing animals is found in Sir Henry Hoyle Howorth’s History of the Mongols, which recounts that Genghis Khan once demanded birds and cats from a besieged city, attaching incendiary material to them to burn the settlement. Some historians note this parallel as an example of how such legends may have influenced Japanese interpretations of the Tsushima events.^[8]

In October 1275, a Mongol fleet of approximately 900 ships and 40,000 men attacked Tsushima and Iki (pages 105, 107, 109). The governor of Tsushima, So‑no‑Sukekuni, and the governor of Iki, Sayemon‑no‑Jo Kagetaka, organised the defence with their garrisons (pages 107, 117). The Mongols employed overwhelming force, siege tactics, and psychological warfare, including the use of war drums to frighten Japanese horses (pages 119-120, 131, 135). Despite fierce resistance, the Japanese defenders suffered heavy casualties, and the Mongols temporarily occupied Tsushima and Iki.^[9]

The Mongol occupation of Tsushima and Iki allowed them to prepare for subsequent operations against Kiushu (pages 120, 131, 180). Earlier interactions with Mongol/Korean envoys, including the capture of Japanese natives, contextualised the escalating conflict (pages 96-97). The islands’ defence demonstrated the importance of local governors and fortifications in delaying invaders — though at a significant human cost (pages 120, 131).^[10]