After the fall of Zhao in 228 BCE, Wang Jian's army stationed in Zhongshan started preparations for an offensive war against Yan. Ju Wu, a Yan minister, proposed to King Xi of Yan to form alliances with the Dai, Qi, and Chu states, and make peace with the Xiongnu in the north, as a preemptive measure in preparation for the Qin invasion. However, Crown Prince Dan felt that the alliance strategy was unlikely to succeed, so he sent Jing Ke to assassinate Ying Zheng, the king of Qin. Jing Ke entered Qin disguised as an envoy, bringing with him a map of Dukang and the head of Fan Wuji, a turncoat Qin general. The assassination attempt failed and Jing Ke was killed. In 227 BCE, using the assassination attempt as casus belli, Ying Zheng ordered Wang Jian to lead an assault against Yan, with Meng Wu as Wang's deputy. The Qin defeated the Yan army as well as Yan's reinforcements from Dai in a battle on the eastern bank of the Yi River, after which they captured the Yan capital, Ji. King Xi of Yan and his son, Crown Prince Dan, fled with their remaining forces to the Liaodong Peninsula. A Qin army led by Li Xin pursued the retreating Yan to the Yan River, where they engaged with enemy forces and destroyed the bulk of Yan army. Later, King Xi ordered Crown Prince Dan's execution and sent his son's head to Qin as an "apology" for the assassination attempt. Qin accepted the offer and did not attack Yan for the next three years. In 222 BCE, Wang Ben led a Qin army to invade Liaodong, destroying Yan's remaining forces, capturing King Xi, bringing an end to the state of Yan. The former territories of Yan were partitioned and re-organised into the Qin dynasty's Yuyang, Beiping, Liaoxi and Liaodong commanderies.
Conquest of Chu
In 224 BCE, Qin began preparations for an invasion of Chu, its most powerful rival among the six states. During a discussion between Ying Zheng and his subjects, the veteran general Wang Jian claimed that the invasion force needed to be at least 600,000 strong to succeed against Chu, but the younger general Li Xin believed that 200,000 men would be sufficient. Ying Zheng put Li Xin in command of the Qin army to attack Chu. The Chu defenders, led by Xiang Yan, took Li Xin's army by surprise with a 500,000 men army and defeated the Qin invaders in the unfamiliar territory of Huaiyang, modern-day northern Jiangsu and Anhui provinces. Xiang Yan achieved victory by luring the Qin army away through allowing them a few initial victories. But then Li Xin's army was surprisingly ambushed by Lord Changping's army. Xiang Yan's army burnt two large Qin camps, and killed seven commandants. This incident was considered the greatest setback out of all of Qin's campaigns. Henceforth, Ying Zheng assigned Wang Jian the command of a 600,000 strong army in the following year as he had requested and ordered him to lead another attack on Chu. High in morale after their victory in the previous year, the Chu forces were content to sit back and defend against what they expected to be a siege of Chu. In response, Wang Jian decided to lull the Chu garrisons into a false sense of security by appearing to idle in his fortifications while secretly training his troops to fight in Chu territory. After a year, a great portion of the Chu garrisons decided to disband and demobilize due to apparent lack of action from the Qin. Wang Jian invaded at this point, having prepared for war the entire time, and overran Huaiyang and the diminished Chu forces. Chu was swept away by the momentum of the swift assault and could only sustain local guerrilla-style resistance until it was fully conquered with the capture of Shouchun and the death of its last leader, who was either Lord Changping or Fuchu depending on different accounts, in 223 BCE. Conflicting narratives of the battle in the Records of the Grand Historian state that Xiang Yan was either killed in action or committed suicide. Thus the state of Chu was brought to an end. In 222 BCE, the Qin army advanced southward and annexed the Wuyue region.
Conquest of Qi
In 264 BCE, Tian Jian ascended the throne of Qi and was assisted by his mother, the queen dowager, in managing state affairs. Qin bribed Hou Sheng, the Qi chancellor, to dissuade King Jian from helping the other states while they were being attacked by Qin. By 221 BCE, Qi was the only state in China that had yet to be conquered by Qin. Qi hurriedly mobilised its armies to its western borders as a safeguard against a possible Qin invasion. In the same year, Ying Zheng used Qi's rejection of a meeting with a Qin envoy as an excuse to attack Qi. Li Xin led the Qin Army along with Wang Ben, avoided direct confrontation with enemy forces stationed on Qi's western borders, and advanced into Qi's heartland via a southern detour from Yan. The Qin forces met with little resistance as they passed through Qi territory and eventually arrived at Linzi, the capital of Qi. King Jian was caught by surprise and, after being persuaded by Hou Sheng, he surrendered to Qin without putting up a fight. The former territories of Qi were reorganised to form the Qin Empire's Qi and Langya commanderies.
Aftermath
He retired after the Qin's unification. He was given the area near modern Gansu.
In popular culture
He, alongside Ying Zheng are protagonists of the Kingdom manga, anime and its 2019 live action film adaptation. In the manga he goes by the name Shin, and later Ri Shin.
