In 369, Huan Wen's Third Northern Expedition marched into Fangtou (枋頭, in present-day western Xun County, Henan), and the capital of Yidu was shaken. The Former Yan lord Murong Wei sent people to rescue Former Qin Jianjian, and after the fact, he ceded the land west of Hu Prison (虎牢, in modern Xingyang, Henan). Wang Meng firmly laid down the strategy of "saving first and taking later" and sent a large army to rescue Former Yan.
Murong Wei used Murong Chui and defeated Huan Wen in September of that year, and the Combined Forces of Yan and Qin killed more than 40,000 enemies. Afterwards, Former Yan broke the treaty and refused to cut off the land, and Former Qin used this as an excuse to cut down Yan. In December, Wang Meng led an army of 30,000 Yan and occupied Luoyang in the first month of the following year, capturing Murong Zang, the king of Yan'an, and occupying Xingyang (荥阳, in modern Xingyang, Henan).
In May 370, Wang Meng, Yang An and 10 other generals led an army of 60,000 to attack Former Yan and marched directly to the capital Yecheng. Wang Meng asked Yang An and others to attack Jinyang, and he himself led his army directly to Huguan. Wang stormed Huguan and captured Murong Yue, the king of Former Yan'an, alive, and all the counties he passed fell by the wind. Jinyang was delayed, and Wang Meng ordered his men to dig tunnels, and the inside and outside should jointly occupy Jinyang, and Murong Zhuang, the king of the Eastern Yan Dynasty, was captured alive.
When Murong Wei learned of the Qin army's attack on Yan, he ordered Murong Ping to lead an army of 300,000 soldiers and horses to meet the enemy, and summoned Li Feng, The Yellow Gate Attendant Lang Liang Chen, and Zhongshu Shilang Le Song to meet him. Murong Wei asked:
"How many people are there in the Qin Army?" When our army is exhausted, will Wang Meng fight with our army? ”
"The qin state is weak, how can it be enemy of our Wang Division?" Wang Meng was not a regular talent, and he was certainly not Tai Fu's opponent, so His Majesty did not have to worry. Li Feng said.
Murong Wei's face was joyful.
"In the future, the soldiers are not brave, and the soldiers are not expensive." The Qin army came from afar, and when we used our strategy to win, why did we hope to surrender without a fight? Liang Chen and Le Song continued.
Murong Wei's face changed. Before he could wait for the slowdown, the news of the loss of Huguan and Shangdang came in, and Murong Wei's face was like earth. Immediately sent Li Feng to urge Murong Ping to march quickly.
Murong Jue's army was preparing to drag down the Qin army with a protracted battle, and the situation was opposed to Wang Meng's army at Luchuan. Murong commented that he had suppressed the enemy with a heavy hand and forbade the army to go to war. Murong Jue ordered his men to occupy the Mountain Spring of Yangu, "ordering the soldiers to enter a horse of silk, and only then did they have to give two stones of water", and the money they received was piled up into a hill.
When Wang Meng learned of this, he couldn't help but sneer:
"Murong Jue is really a puppet, even if there are millions of people, they are not afraid, let alone only two or three hundred thousand troops?" It seems that I will be able to destroy Yan yan in one fell swoop on this trip. ”
Wang Meng asked the guerrilla general Guo Qing to lead five thousand cavalry, and the night attack on the Yan army had a heavy grain and grass, and burned it. The skyrocketing fire could be seen even by the officials and people of the capital City of Yecheng. Murong Wei sent people to Luchuan and issued an edict rebuking Murong Wei:
"The great king is the son of Gaozu, why doesn't he put the country's social welfare first, but instead sells spring water to make the country rich?" He shared the treasury with the king, so why did he still worry about being poor? Quickly scatter the money and wealth back to the three armies, boost morale, and pacify the Qin army in one fell swoop. ”
Murong Jue received the edict and had to send a letter of war to Wang Meng. On the day of the decisive battle, Wang Meng made a generous statement in front of the battle, and the soldiers all rubbed their fists together, and their morale was high for a while.
The Qin generals Deng Qiang, Zhang Oyster, and Xu Cheng led an army to rush into the Yan army, and the Yan army, after Murong Comment's tumultuous operation, had already lost all morale and only wanted to escape. By noon that day, Murong Ping was defeated, the Qin army beheaded more than 50,000 people, more than 100,000 troops fled, and 60,000 or 70,000 prisoners were taken prisoner, and Murong Pingdan fled back to Yicheng.
The Battle of Luchuan almost defeated the Former Yan family. In November, Former Qin destroyed Former Yan, less than a year after Murong Chui was forced to flee.