The Battle of Baekgang and the Jinshin War

After the Taika Reforms, Japan suffered a major defeat fighting the Tang-Silla alliance on the Korean Peninsula. Later, the Jinshin War broke out over imperial succession at home. Let us examine the turbulent latter half of the 7th century.

Basic Knowledge

In the middle of the 7th century, Silla formed an alliance with Tang, destroyed Baekje in 660 and Goguryeo in 668, and moved toward unifying the peninsula. In response, Japan (Wa) sent a large army to the Korean Peninsula in 663 to support the restoration of Baekje, its ally.
This was the Battle of Baekgang. The Japanese army fought the Tang-Silla allied forces at the Baekgang River (on the present-day western coast of the Korean Peninsula) and suffered a major defeat. The Japanese navy was burned, and many soldiers died in battle.
After the defeat, Prince Naka no Ōe established a defensive system in preparation for a Tang invasion:
・Mizuki: A defensive facility protecting Dazaifu (Fukuoka Prefecture)
・Ōno Castle: A mountain castle protecting Dazaifu
・Beacon fires and Sakimori: A system of guards
In 667, the capital was moved to Ōmi Ōtsu Palace, and in 668 Prince Naka no Ōe ascended the throne and became Emperor Tenji.
After Emperor Tenji’s death, the Jinshin War broke out in 672. This was a struggle for imperial succession between Emperor Tenji’s younger brother, Prince Ōama, and his son, Prince Ōtomo. Prince Ōama won and ascended the throne as Emperor Tenmu.

Further Study (Background・Impact)

Defeat in the Battle of Baekgang was a shocking event for Japan. Japan, which had held influence in the southern Korean Peninsula until then, was forced to withdraw completely from the peninsula. This event can also be said to have determined Japan’s direction of building a state within the “Japanese Archipelago.”
At the same time, Japan rapidly developed a defensive system in preparation for a Tang invasion. The Mizuki built in front of Dazaifu was an earthen fortification about 1.2km long and about 9m high, parts of which still remain today. Mountain castles (Korean-style mountain fortresses) were built throughout Kyushu, and Sakimori guards were stationed there.
The Jinshin War, which occurred in 672, was the largest civil war in ancient Japan. Prince Ōama, the younger brother of Emperor Tenji, had become a Buddhist monk and lived in seclusion in Yoshino after the emperor’s death. Fearing that his nephew, Prince Ōtomo, Emperor Tenji’s eldest son, would ascend the throne, he raised an army. With the support of powerful clans in the eastern provinces (Mino and Owari), he defeated the Ōmi court in a battle lasting about one month.
Emperor Tenmu held strong power and promoted the construction of a full-scale ritsuryō state. He is considered to have been the first to use the title “emperor” instead of “Great King,” and the country name “Japan” is also considered to have begun to be used around this time. After his death, his empress, Empress Jitō, ascended the throne, established the Asuka Kiyomihara Code in 689, and moved the capital to Fujiwara-kyō in 694. Fujiwara-kyō was Japan’s first full-scale city with a grid street system and became the model for later Heijō-kyō and Heian-kyō.

Points to Note (Easy to Confuse)

① The Battle of Baekgang (663) is pronounced “Hakusukinoe” or “Baekgang.” Textbooks differ. ② The fall of the Three Kingdoms of Korea: Baekje (660) → Goguryeo (668) → Silla unification (676). ③ The Jinshin War occurred in 672. Remember the correspondences: Prince Naka no Ōe = Emperor Tenji, and Prince Ōama = Emperor Tenmu. ④ Do not confuse “Mizuki” with “Mito.” Mizuki was a defensive facility protecting Dazaifu. ⑤ The “Asuka Kiyomihara Code” was established in 689, while the “Taihō Code” was established in 701. Be careful about the difference. ⑥ Empress Jitō moved the capital to Fujiwara-kyō in 694, while Emperor Genmei moved the capital to Heijō-kyō in 710. Do not confuse them.

Practice

1. What was the name of the battle in 663 in which Japan suffered a major defeat on the Korean Peninsula?
2. What was the name of the person who won the Jinshin War in 672 after ascending the throne?
3. Name two defensive facilities Japan built after the Battle of Baekgang.