The Battle of Baekgang, also known as Battle of Baekgang-gu or by the Japanese name Battle of Hakusukinoe (白村江の戦い Hakusuki-no-e no Tatakai or Hakusonkō no Tatakai), was a battle between Baekje restoration forces and their ally, Yamato Japan, against the allied forces of Silla and the Tang Dynasty of China. The battle took place in the lower reaches of the Geum River in Jeollabuk-do province, Korea. The Silla-Tang forces won a decisive victory, forced Yamato Japan to withdraw completely from Korean affairs and crushed the Baekje restoration movement.
In 660 A.D., the Korean peninsula was divided into three kingdoms, called Baekje, Silla and Goguryeo. These three kingdoms had constantly fought with each other for control of the peninsula for several centuries up to that point. Furthermore, Goguryeo had been engaged in constant wars with the Chinese Sui and Tang dynasties in addition to the aforementioned two Korean kingdoms. While the three Korean kingdoms were not always perpetual enemies, their alliances frequently shifted; a kingdom would become allies with one of the other two, only to later turn against that kingdom and (sometimes) become allies with the other kingdom against whom it had fought earlier. For instance, Silla and Baekje would be allied against Goguryeo (as they were from the late 420's to the early 550's), and later Silla (or Baekje) would betray the other (as happened in 553 AD, when Silla wrested control of the entire Han River basin from Baekje).
Silla had an ongoing alliance with the Tang Dynasty dating roughly to the Tang rise to power in the 620's AD. The Tang made a series of assaults against Goguryeo, but were never able to conquer it. All the Tang invasions had been from the north attacking the south. Tang decided that the best strategy might be to attack Goguryeo from both the northern front and a southern front simultaneously with their ally Silla. However, in order to do this, they (Tang and Silla) had to eliminate Goguryeo's nominal ally Baekje and secure a base of operations in southern Korea for a second front.
Together, Silla and Tang invaded Baekje and effectively eliminated it when they captured the capital of Sabi, as well as Baekje's last king, Uija, and most of the royal family. Soon afterwards, however, the Baekje people revolted and threw off Silla and Tang rule in large areas of northern Baekje. The Baekje general Boksin attempted to take back the 40 lost counties. He also recalled Prince Buyeo Pung from Japan, sent 100 Tang prisoners to the Yamato court and requested military aid. General Boksin proclaimed Prince Buyeo Pung as the new king of Baekje. Although the restoration forces had some initial success against Tang and Silla troops, by 662, they were in serious trouble and their area of control was confined to the fortress of Churyu and its immediate surroundings. As their situation went from bad to worse, Buyeo Pung had Boksin killed for fear of insurrection.
Baekje and Yamato Japan had been long-standing allies and their royal houses had blood relations. The fall of Baekje in 660 came as a terrible shock to the Yamato royal court. Empress Saimei had said:
"We learn that in ancient times there have been cases of troops being asked for and assistance requested: to render help in emergencies, and to restore that which has been interrupted, is a manifestation of ordinary principles of right. The Land of Baekje, in its extremity, has come to us and placed itself in our hands. Our resolution in this matter is unshakable. We will give separate orders to our generals to advance at the same time by a hundred routes."
Crown Prince Naka no Ōe, later to become Emperor Tenji, and Empress Saimei decided to dispatch an expeditionary force led by Abe no Hirafu (阿倍比羅夫) to help the Baekje restoration forces. The troops were drawn from local strongmen (kuni no miyatsuko) from mostly western Honshū, Shikoku, and especially from Kyūshū, though some warriors were also from Kantō and northeastern Japan.
Empress Saimei moved the capital to the Asakura temporary palace near the shipyards in northern Kyūshū to personally oversee the military campaign. As the main fleet set sail, Empress Saimei composed a tanka (Japanese poem of thirty-one syllables) that many scholars believe shows a sense of hope as well as anxiety:
"Waiting for the moonrise to set sail at 'Nikitatsu', It fortunately become a high tide to put up to sea"
The Empress died shortly after the last waves of Yamato troops departed for Korea. The Crown Prince (Tenji) carried her remains back to Asuka. The Crown Prince, dressed in white mourning clothes, set up his residence in the Nagatsu temporary palace in Kyūshū, and continued to oversee the expeditionary operation.
Around August 661, 5,000 soldiers, 170 ships, and the general Abe no Hirafu, arrived in Baekje restoration controlled territory. Additional Japanese reinforcements, including 27,000 soldiers led by Kamitsukeno no Kimi Wakako (上毛野君稚子) and 10,000 soldiers led by Iohara no Kimi (廬原君), arrived in 662
In 663, Baekje restoration forces and the Yamato navy convened in southern Baekje with the intent to relieve the capital of the Baekje restoration movement in Churyu, which was under siege by Silla forces. The Yamato navy was to ferry ground troops to Churyu via the Geum river and lift the siege. However, Tang also sent 7,000 soldiers and 170 ships to blockade Yamato reinforcements from relieving the capital. On August 27, 663, the advance guard of the Japanese fleet tried to force their way, but Tang ships held firm, repelled the attacks and maintained disciplined ranks.
On the second day of the battle, the arrival of Japanese reinforcements made their forces several times larger than the Tang fleet arrayed against them. However, the river was narrow enough where the Tang fleet could cover their front and protect their flanks as long as they maintained their ordered battle lines. The Japanese were confident in their numerical superiority and attacked the Tang fleet at least three times throughout the entire day, but the Tang fought off each attack. Towards the end of the day the Japanese became exhausted and their fleet lost cohesion through their repeated attempts to break through Tang lines. Sensing the right moment, the Tang fleet moved reserves and counterattacked, breaking both the left and right flanks of the Japanese, enveloping their fleet and crowding in the ships so they could not move or retreat. Many Japanese fell into the water and drowned and many of their ships were burned and sunk. The Yamato general Echi no Takutsu was killed after striking down more than a dozen men in close quarters combat.
Japanese, Korean and Chinese sources all point to heavy Japanese casualties. According to the Nihon Shoki, 400 Japanese ships were lost in the battle. Chinese sources claim 10,000 Japanese deaths.
Silla participation in the battle involved cavalry forces that defeated Baekje restoration ground troops that were supporting the Yamato navy on the banks of the river. It is unclear as to whether or not this took place before the Japanese navy went to battle Tang ships or during.
Without Yamato troops to lift the siege, the fortress of Churyu surrendered to Silla and Tang forces in September 7, 663. Buyeo Pung took a boat and fled with several followers to Goguryeo.
The Battle of Baekgang was Japan's greatest defeat in its premodern history. Japan's losses were enormous and there would be no state-sponsored troop deployments to Korea for over 900 years (until Hideyoshi's invasions of Korea in the late 16th century). Japan also lost a key ally on the East Asian continent in Baekje as well as a direct link to continental technology and culture. Due to the scale and severity of their defeat, the Yamato court would fear an invasion from Tang or Silla or both and built a huge network of shore fortifications throughout the rest of the 600's. In 664, the Yamato court established frontier guards and signal fires in Tsushima Island, Iki Island, and northern Kyushu. Also embankments storing water were built around the fortresses in Kyushu which were called the Water Fortress. In 665, the Yamato court sent Baekje generals and artisans to construct a rampart in Nagato province, and two ramparts in Kyūshū. In 667, a rampart was constructed in the Yamato region, another one at Sanuki, and yet another at Tsushima island. The Japanese would continue to build fortifications until 701.
For Baekje, the battle was the knockout blow that ended any hope of reviving the kingdom. Many Baekje people defected to either Goguryeo or Japan. Baekje royalty who fled to Japan were given the same ranks and titles in the Yamato court and Baekje refugees were given de facto citizenship status or special artisan status.
The victory gave Silla control of all former Baekje lands in Korea and a secure base for the Tang in southern Korea to launch a two-pronged invasion of Goguryeo. The Silla-Tang alliance first launched attacks on Goguryeo from the south in 661 and the Goguryeo capital at Pyongyang finally fell in 668.
The battle also introduces interesting questions regarding Japan's relations with the Korean states and their level of development at the time. For example - why did the Japanese fare so badly against Silla and Tang armies? According to several scholars, it is clear that in the 7th century, the Chinese and Koreans had better weapons and more importantly, their troops and officers were better trained and disciplined. Despite years of reforms modeled after mainland examples from China and the Korean Peninsula, the Yamato armies did not adopt the organized infantry tactics of Chinese and Sillan armies. Furthermore, Yamato Japan was still a nascent and developing state run in practice by local strongmen (though in theory by the royal court) and without any real form of unified command. In addition, Japanese soldiers were drawn from many corners by local "strongmen" that controlled their own territories. It is also doubtful that, among the Japanese, there was much standardization in either weapons or unit tactics.
Another interesting question that has puzzled many scholars is - why did Yamato go through so much effort to protect Baekje? Bruce Batten sums it up by saying:
"Why the Japanese should have thrown themselves with such vigor into a war that, if not quite an intramural Korean conflict, had at least no direct bearing on Japanese territory, is not easy to answer."
The battle, as well as all the preparation behind it, shows clearly (aside from any other documentation) that there were strong ties between Yamato Japan and Baekje of Korea that might have been beyond the obvious military, political and economic interests that are regularly shared between states.