Conflict in 645 Emperor Taizong of
Tang used
Yŏn Kaesomun's murder of
King Yeongnyu of Goguryeo as the pretext for his campaign and started preparations for an invasion force in 644. General
Li Shiji commanded an army of 60,000 Tang soldiers and an undisclosed number of tribal forces which gathered at
Youzhou. Emperor Taizong commanded an armored cavalry force of 10,000, which eventually met up and joined general Li Shiji's army during the expedition. A fleet of 500 ships also transported an additional 40,000 conscripted soldiers and 3,000 military gentlemen (volunteers from the elite of
Chang'an and
Luoyang). This fleet sailed from the
Liaodong Peninsula to the
Korean Peninsula. In April 645, general
Li Shiji's army departed from Yincheng (present-day
Chaoyang). On 1 May, they crossed the
Liao River into
Goguryeo territory. On 16 May, they laid siege to Gaimou (Kaemo), which fell after only 11 days, capturing 20,000 people and confiscating 100,000
shi (6 million liters) of grain. Afterwards, general
Li Shiji's army advanced to Liaodong (Ryotong). On 7 June, they crushed a Goguryeo army of 40,000 troops that had been sent to the city to relieve it from the Tang siege. A few days later,
Emperor Taizong's cavalry arrived at Liaodong. On 16 June, the Tang army successfully set Liaodong ablaze with incendiary projectiles and breached its defensive walls, resulting in the fall of Liaodong to the Tang forces. However,
Emperor Taizong sent general
Li Shiji with 15,000 troops to lure the Goguryeo forces. Meanwhile, another Tang force secretly flanked the Goguryeo troops from behind. On 20 July, the two sides met at the
Battle of Jupilsan and the Tang army came out victorious. After weeks passed, Emperor Taizong considered abandoning the siege of Ansi to advance deeper into Goguryeo, but Ansi was deemed to pose too great of a threat to abandon during the expedition. Eventually, the Tang staked everything on the construction of a huge mound, but it was captured and successfully held by the defenders despite three days of frantic assaults by Tang troops. Facing worsened conditions for the Tang army due to cold weather (winter was approaching) and diminishing provisions, Emperor Taizong was compelled to order a withdrawal from Goguryeo on October 13. He left behind an extravagant gift for the commander of Ansi Fortress. Tang Taizong's retreat was difficult and many of his soldiers died. Taizong himself tended to the injuries of the
Göktürk generals
Qibi Heli and
Ashina Simo, who were both wounded during the campaign against Goguryeo.
Conflicts in 654–668 and fall of Goguryeo Under
Emperor Gaozong's reign, the Tang Empire formed a military alliance with
Silla. When
Goguryeo and
Baekje attacked Silla from the north and west respectively,
Queen Seondeok of Silla sent an emissary to the Tang Empire to request military assistance. In 653, Baekje allied with
Yamato Wa. Even though Baekje was allied with Goguryeo, the
Han River valley separated the two states and was a hindrance in coming to each other's aid in time of war.
King Muyeol assumed the Silla throne in 654. Between 655 and 659, the border of Silla was harassed by Baekje and Goguryeo; Silla therefore requested assistance from Tang. In 658, Emperor Gaozong sent an army to attack Goguryeo King Muyeol suggested to Tang that the Tang–Silla alliance first conquer Baekje, breaking up the Goguryeo–Baekje alliance, and then attack Goguryeo. The Baekje capital
Sabi fell to the forces of Tang and Silla. The king and the crown prince were sent as hostages to the Tang Empire. The Tang Empire annexed the territory and established five military administrations to control the region instead of Silla, which was painfully accepted. In a final effort, general
Gwisil Boksin led continued resistance against Tang occupation of Baekje. He requested military assistance from
Yamato allies. The
Nihongi Chronicles notes that during his pleas for Yamato assistance, Prince
Buyeo Pung was conferred the cap of shiki given the younger sister of Komoshi Oho no Omi to wed.
Emperor Tenji of Japan sent Ajimasa Sawi no Muraji of Lower Daisen Rank, and Takutsu Hada no Miyakko, in command of four thousand men to escort Prince Buyeo Pung back to his country where General Gwisil Boksin met and entrusted the governance of the land to the prince. The Tang fleet, comprising 170 ships, advanced towards Chuyu and encircled the city at the
Baekgang River. As the Yamato fleet engaged the Tang fleet, they were attacked by the Tang fleet and were destroyed. In 663, the Baekje resistance and Yamato forces were annihilated by the Tang and Silla forces at the
Battle of Baekgang. Subsequently, Prince
Buyeo Pung of Baekje and his remaining men fled to Goguryeo. The natives rebelled and besieged Liu Renyuan in the capital until
Liu Rengui could bring in reinforcements. A stalemate ensued, with Baekje holding some cities while Silla and the Tang occupied others. In the autumn of 663, a combined Tang-Silla army marched for Chuyu, the capital of the rebels. Chuyu was captured on 14 October and the rebellion was vanquished. In the summer of 661,
Su Dingfang led an army of 44,000 across the sea and laid siege to
Pyongyang while another Tang army under
Qibi Heli advanced overland. The Tang army was 350,000 strong and Silla was only requested to provide supplies during this expedition. Qibi Heli defeated a Goguryeo army at the
Yalu River but Su Dingfang failed to take Pyongyang. The invasion was called off in February 662 after failing to take Pyongyang for several months and when a subsidiary Tang force led by Pang Xiaotai was defeated by
Yŏn Kaesomun at the
Battle of Sasu. Yŏn Kaesomun's death paved the way for a fresh invasion by Tang and Silla in 667, this time aided by Yŏn Kaesomun's oldest son. The alliance with Silla also proved to be invaluable, thanks to the ability to attack Goguryeo from opposite directions, and both military and logistical aid from Silla. ==Aftermath==