1September, 2004, Xiao Yanyan and his son led 200,000 troops south again in the name of recovering the lost land of the three passes (i.e. Waqiao Pass, Yijin Pass and Meiyukou Pass) captured by Chai Rong in Zhou Shizong. LiLin Xiao, the pioneer general of Liao Dynasty, led the military forces, took the lead, defeated Song Jun such as Tang Xing and Sui Cheng, and soon advanced into Wang Du, reaching Dingzhou.
Although Song Zhenzong made full preparations to resist the southward movement of Liao troops, he formulated a strategy of avoiding Liao's sharp edge and luring the enemy in depth, and deployed troops to meet the enemy in Hebei and Hedong. However, the massive invasion of Liao soldiers gave Song Ting a great shock, and Song Zhenzong quickly called ministers to discuss the strategy of retreating the enemy. In the Song Dynasty, ministers disagreed on how to meet the enemy. Some people suggested that the late Zhenzong take refuge in Jinling (now Nanjing), while others suggested that Song Zhenzong take refuge in Chengdu. Only Prime Minister Kou Zhun insisted on meeting them.
The old minister of Song Zhenzong Yinfu took his father and son to the south, and constantly told them about the benefits of reconciliation between Liao and Song Dynasties, which moved his father and son very much. In fact, Xiaoyan and her son have long had the idea of making peace with Song, just looking for the right time. Seeing that Liao and Song were constantly persuaded to make peace, the soldiers split into two ways. Continue to conquer the Song land with soldiers and exert pressure; ⑤ Sign for communication with Song Ting to convey the message of reconciliation between Liao and Song Dynasties.
In the battle of single-source alliance, the Khitan chose the strategy of avoiding the heavy and taking the light. At the beginning of the war between the two countries, after Liao entered Hebei, he lost several siege attacks. This exposed the lack of good defense and Liao's ability to attack the enemy, so the Qidan army ignored some heavily stationed cities in Hebei, bypassed these cities directly, and went straight all the way, which might soon force the troops to capture Yuzhou.
Song Zhenzong's personal expedition to the Forbidden City reflected Song's determination. At this time, the unexpected death of the pioneer marshal of Liao country also dampened the morale of Liao country. In addition, Song Jun of Yanmenguan took advantage of the opportunity of the Liao army going south to enter the Liao country to contain it. Although Liao bypassed the important town of Hebei, there were many Song Jun behind it. The situation of Liao army is not completely dominant. If we can't defeat the naming country in a short time, we may even be cut off by Song Jun, so in this case where both sides have scruples, the single-source alliance was born.