After the establishment of the Northern Song Dynasty, although it was basically unified, it still faced off with two regimes, one was the Khitan in the north and the other in the northwest was the Western Xia. During the Song Dynasty, the Northern Song Dynasty and the Khitan reached an "alliance of the Yuanyuan" to achieve peaceful coexistence, but the Western Xia had always been enemies of the Northern Song Dynasty, and the two sides had fought a border war for more than a hundred years intermittently! So who caused the war with the Western Xia?
Although the Western Xia was founded in 1038 by the Dangxiang clan leader Yuan Hao, it was formed with LiangZi of the Northern Song Dynasty as early as 982! For the Northern Song Dynasty, the person who triggered this war was Zhao Guangyi, the Emperor taizong of the Song Dynasty! Things have to start from the predecessor of the Western Xia, the Dingnan Army. It is said that in the last year of the Tang Dynasty, after Huang Chao led the rebel army to invade Chang'an, Tuoba Sigong, the leader of the Dangxiang clan, led the army to fight against the peasant army. Later, Emperor Tang rewarded Tuoba Sigong heavily, gave him the surname Li (李氏), and added the title of Envoy of the Difficult Army.
Since the end of the Tang Dynasty, Tuoba Sigong and his descendants have been occupying the northwest region, "Tongyin, Xia, Sui, You, and Jing five prefectures". However, they did not claim the title of emperor, and still paid tribute to the Central Plains Dynasty, and their attitude was quite obedient. When news of the establishment of the Northern Song Dynasty reached Xia prefecture, the leader Li Yixing immediately sent his nephew to pay tribute. After that, Dang Xiang often provided warhorses to the Northern Song Dynasty to help them fight against the Northern Han Dynasty, and the relationship was very harmonious.
However, after Emperor Taizong of Song ascended the throne, his attitude towards the dangxiang people changed. For example, in 978, after the death of Li Kerui, the envoy of Jiedu of The Dingnan Army, Emperor Taizong of Song did not follow the custom and made Li Jijun, the son of Li Kerui, the emissary of Jiedushi, but appointed him as the emissary of Jiedushi. Although the number of words in the official position is more, the meaning is different, and the observation of the festival is actually the meaning of the temporary festival envoy, the implication is that this is only a temporary appointment, because Song Taizong is waiting for an opportunity.
Two years later, Li Jijun fell ill and died, so his son was young, so the post of Jiedu Observation was inherited by Li Jijun's younger brother Li Jifeng. It was precisely because of Li Jipeng's succession that it caused dissatisfaction within the clan. There were many contradictions within the party, and some people coveted wealth and wealth, and suggested to Emperor Taizong of Song that Li Ji be recruited to join the dynasty. Song Taizong was naturally very happy, so he moved Li Jipeng to Kaifeng, and at the same time controlled the territory of the Dingnan Army.
Song Taizong seems to have achieved "land reform" and officially incorporated the five northwestern states into the territory of the Northern Song Dynasty, but this was only the beginning of the war! Some people within the Dangxiang aristocracy were reluctant to accept the rule of the Northern Song Dynasty, and they gathered under Li Jiqian's command and rebelled against the Song. At the end of 982, Li Jiqian attacked Xiazhou, and his war with the Northern Song Dynasty officially broke out. Li Ji's initial mobilization was not smooth, and it was not until 985 that he began to gradually grasp the situation on the battlefield and recover the original five states.
After Li Jiqian's death, his son Li Deming took the throne, and relations with the Song Dynasty began to ease, and he devoted himself to marching westward, successively occupying Liangzhou and Ganzhou. After Li Deming's death, Yuan Hao took the throne, and he broke with the Northern Song Dynasty again, and a war broke out between the two sides that lasted for several years, and the Northern Song side lost all three major wars, losing tens of thousands of elite soldiers. It was only later that the two sides reached a "celebration of the calendar and peace talks". However, the Western Xia and northern Song Dynasties did not maintain peace, and the border conflicts between the two sides never stopped.
During the reign of Emperor Yingzong of Song, a battle broke out between the two sides. During the reign of Emperor Shenzong of Song, he mobilized the Five Roads Army to attack Western Xia, but was defeated. After the Battle of Yongle City, the losses of the Song army were even more heavy. During the reign of Emperor Zhezong of Song and Emperor Huizong of Song, the war between the Northern Song Dynasty and the Western Xia did not stop, but the Northern Song Dynasty began to gain the upper hand. It was not until 1119, after the Song army captured the Hengshan region, that the Western Xia asked the Northern Song for peace, and the two sides were considered to be dismissed. However, at this time, the Northern Song Dynasty was less than eight years away from its demise.
References: 1. History of the Song Dynasty; 2. History of the Relationship between the Song and The Xia