Conquests of Yu and Guo
The neighboring State of Guo frequently attacked the border of Jin. Duke Xian wished to overthrow Guo, but needed passage through the State of Yu (虞國), which was allied with Guo, to do so. On the advice of his officer, Xun Xi (荀息), Duke Xian sent beautiful women to the Duke of Guo and a beautiful young man to the Duke of Yu with instructions to distract the rulers from government affairs. At the same time, men were sent to cause trouble on Guo's northern border.
As expected, officials in Guo blamed Duke Xian for the new trouble they were encountering on the northern border. Feigning insult, Duke Xian sent officer Xun Xi to the State of Yu to request passage so that they could avenge the insult. Bringing gifts of jade and horses, Xun Xi arrived in the State of Yu to request passage. Under the influence of his new beloved, the Duke of Yu immediately agreed, over the protestations of his own official, Gong Zhiqi (宮之奇). Gong Zhiqi described the relationship of Yu and Guo with the Chinese proverb "The teeth are cold when the lips are lost" (Chinese: 唇亡齿寒; pinyin: Chún Wáng Chǐ Hán). He told the Duke of Yu that if Guo were conquered, Yu would be next. The Duke of Yu ignored his warning and Gong Zhiqi secretly left the state of Yu, foreseeing its destruction.
In 658 BC, the 19th year of his reign, Duke Xian of Jin sent his general Li Ke and his officer Xun Xi to attack the State of Guo during the reign of Duke Chou of Guo (虢公醜). Ever more favorable to Jin, the Duke of Yu assisted in the invasion. He sent his own army to capture Xiayang Pass (下陽關) for Jin, under the ruse that his army was there to subdue the rebellious Quanrong tribe.
In the winter of 655 BC, the 22nd year of his reign, the State of Guo was conquered by Jin. The Duke of Yu was given a part of the women and treasures sacked from Guo. Li Ke was then granted permission to station the Jin army outside the Yu capital to rest. After a few days, the Duke of Yu was suddenly informed that Duke Xian of Jin was outside the city wall of the Yu capital. The Duke of Yu quickly went out to greet him and Duke Xian of Jin invited the Duke of Yu to the Ji Mountain (箕山) to hunt. In an ostentatious display, perhaps still under the influence of the beloved planted at his court by Duke Xian, the Duke of Yu brought the entire military force stationed in the capital to the hunt in the Ji Mountain.
While hunting, the Yu officer Baili Xi reported to the Duke of Yu trouble at the capital. By the time the Duke of Yu arrived at the outskirts of the city, the Yu capital has already been captured by the Jin army. The Duke of Yu and Baili Xi were held captive and brought back to the State of Jin. Baili Xi was recognized as a good officer by Duke Xian of Jin but Baili Xi rejected every offer given to him to become a court official of Jin. He was later given to the state of Qin as a servant dowry with Princess Bo Ji (伯姬). (The use of Yu to attack Guo was one of the Thirty-Six Stratagems).
