Yamataian takeover of Daifudou

The Yamataian takeover of Daifudou, also known as the Yamataian invasion of Daebudo (대부도 침입) or the Byeongo Expedition (병오 동정) in Yeongseoneo, was a 1478 invasion launched by the Morikawa Clan of the Yamataian Empire against Yeongseonese pirate bases on Daifudou island, also known as Daifujima or Daebudo, located between Yamatai and Yeongseon. The Yeongseoneo identifying phrase derives from Byeongo in the sexagenary cycle used in the Cheonhae dynasty of Yeongseon. The identifying phrase collocates with the year 1478 in the Gregorian calendar year.

Background
The modern island of Daifudou, known as Daebudo in Yeongseoni, lay on the crucial trade route between Yashima and Yeongseon for centuries. The island's economy relied heavily on trade with both Yamatai and the nearby Yeongseoni kingdoms. In 1145, the island came under the influence of the Kingdom of Cheonhae during the reign of King Yangjong, with the ruling Jongmu Ki clan entrusted with official diplomatic and trade negotiations with Yamatai and other the northern Yashiman states. Daebudo was never fully incorporated into Cheonhae, and the rulers of Daebudo enjoyed special privileges and autonomy exclusive to their domain due to distance between Daebudo and the royal capital of Goseong.

In the 14th century, pirates based in northwestern Yeongseon began carrying out raids against trading vessels as well as attacks against southern Yamatai and other places in the Sea of Yashima, such as Fujishima. In 1329, the Kingdom of Cheonhae and local lords in Northern Yeongseon carried out a campaign to suppress the pirate activity in northern Yeongseon at the request of the Imperial Court of Yamatai, which was occupied with fighting the Mizuho War at the time. Though piracy died down for a period, the collapse of the Cheonhae Kingdom in 1368 and the beginning of the Warring States Period of Yeongseon (1368-1547) allowed pirates to re-establish themselves in the area.

Lord Ki Yang-Gu of Daebudo passed away in 1421, with the throne falling to his infant son Ki Tae-Woong. Power was quickly seized by Ki Mi-Jun, the younger brother of Ki Yang-Gu, who was a powerful pirate warlord that enabled the establishment and expansion of pirate bases and operations in Daebudo. Ki Tae-Woong and retainers loyal to him fled to Yamatai, where they were harboured by Shugo Morikawa Tanehide, whose territories were in the south of Yamatai and were often subjected to pirate raids.

In 1434, General Kotomine Tomotane, a retainer of Morikawa Tanehide, carried out an attack on the pirate bases in Daebudo. The Kotomine Expedition burned 121 ships and rescued more than 100 Yamataian captives. Another campaign was launched in 1446 by Nijimura Yasunao, an official of the Imperial Court. However, this did not stop the pirate attacks and in 1478, Shugo Morikawa Nobumitsu decided to launch an expedition to remove Ki Mi-Jun from power and restore Ki Tae-Woong as the rightful ruler of Daebudo. Morikawa Takeyasu, the third son of Morikawa Nobumitsu, was ordered to oversee the invasion of Daebudo.

Invasion
General Morikawa Nobumitsu left Danbara towards Daebudo on May 15, 1478, with a fleet of 223 ships and 5,823 soldiers. The fleet arrived at Ahngo Bay by the following day. Morikawa dispatched a few scout vessels to draw the pirates out of the bay, a move which succeeded, resulting in a brief exchange that sunk most of the pirate fleet. Several captives were taken, but the island's defences were alerted. Morikawa then sent some captured pirates to demand a surrender. When no reply was received by the noon of May 19, he began shelling the island's defences with cannons before deploying troops to land at the northern end of the island. The Yamataian troops proceeded to raid and plunder the pirate settlements, allegedly including the homes of villagers.

In his diary, Morikawa Nobumitsu claimed that the first day of fighting resulted in the burning of 1879 houses, the capture of 78 ships, the killing of 187 people, the capture of 26 people, and the rescue of 133 Yamataian and Yeonseoni captives held from prior raids. However, 211 Yamataian troops were killed. It is estimated that Yamatai lost between 300 to 867 troops while Daebudo lost between 1,379 to 2,000 troops throughout the invasion.

On 25 July, the Morikawa troops besieged Suro Castle, the seat of the Ki Clan, and captured Ki Mi-Jun on 29 July. Ki Mi-Jun officially surrendered and abdicated from his lordship and Ki Tae-Woong was restored as the Lord of Daebudo. Ki Mi-Jun was later beheaded for his betrayal.

Aftermath
Minor insurgencies broke out on Daebudo after the capture of Ki Mi-Jun, but pirate activities declines rapidly after the Yamataian takeover. Ki Tae-Woong was restored as the ruler of Daebudo and was given similar rights and privileges as granted under the Cheonhae dynasty with the expectation of using his powers to suppress any future pirate activities in the island. In addition, Ki Tae-Woong and the rulers of Daebudo from then on paid tribute to the Yamataian Morikawa Clan and later the Second Empire of Yamatai, before finally being directly annexed by Yamatai in 1832. Yamataian forces and traders also began operating on the island, increasing the Yashiman population greatly, and the Morikawa Clan would maintain a garrison there for centuries.

The Cheonhae Royal Court reacted negatively to the Yamataian invasion, and King Gonyul demanded that Yamatai withdraw its forces from Daebudo. However, the Cheonhae's de facto powers were largely limited to the city of Goseon, and his decree carried little weight outside of the capital. Furthermore, the Yamataian Imperial Court declared no part in the invasion, which was carried out unilaterally by the Morikawa Clan. As Yeongseon was still in the middle of a civil war, no serious attempts were made by Yeongseoni polities to retake Daebudo from Yamatai. After the formation of the Kingdom of Yeongseon by Taejo Yi Myeong-Do in 1547, the new kingdom did little with regards to the status of Daebudo, focusing on the reconstruction of Yeongseon.

The Morikawa intervention on Daebudo marked a new low point in the decline of the Yamataian Imperial Court's influence and power, which would only be eroded further following the disastrous Shinbi War in 1452. This loss of power in favour of autonomous Shugo and the growth of feudalism ultimately resulted in the Kōjutsu War, after which the Hinoan Taikun would take over de facto control of Yamatai.

In the modern day, some Yeonseoni people still consider Yamatai's control of Daifudou as unlawful. However, only fringe elements of Yeongseon's society, especially far right and irredentist organizations would actually advocate for reclaiming Daebudo as part of Yeongseon.