How much Sima Guang hated Wang Anshi, Wang Anshi didn't want an inch of the territory he built, and gave it all to Western Xia. Sima Guang was a famous minister of the Northern Song Dynasty, and his "Zizhi Tongjian" was highly praised by later generations. A person who is so admired, but he almost became a thief. So what's going on here?What is the deep hatred between Sima Guang and Wang Anshi?
Sima Guang and Wang Anshi were originally friends, but Sima Guang belonged to the conservative faction, Wang Anshi belonged to the reformers, and their different political positions led to the two finally turning against each other. During the Song Dynasty, the emperor was very supportive of Wang Anshi's reforms. After Sima Guang went to the table many times to stop him to no avail, he was disheartened and asked for an errand to be released. It was during this period that he edited the "Zizhi Tongjian", the fundamental purpose of which was also to one day abolish Wang Anshi's reform and stabilize the Song Dynasty. Since the founding of the Song Dynasty, there have been three deep enmities, namely the Western Xia, the Tibetan and the Liao State. In particular, the Western Xia harassed the border of the Song Dynasty all the year round, and the years of war made the Song Dynasty's treasury empty and the military salary expenditure was stretched. In order to solve the urgent need of the empty treasury, Wang Anshi proposed a change, but it did not attract enough attention from the imperial court at that time. After Song Shenzong succeeded to the throne, he believed that changing the law was indeed a way to make the Song Dynasty from weak to strong. He activated Wang Anshi and supported his drastic changes. Wang Anshi proposed that if the treasury was to be full, it was first necessary to expand the territory and break the three-sided ring barrier formed by the Liao, Western Xia and Tubo against the Song Dynasty at that time. Wang Shao, who followed Wang Anshi's reforms, proposed a strategy to recover the two states of Hehuang in order to cut off the connection between Western Xia and Tibet, so that Western Xia was completely isolated and helpless. Song Shenzong very much agreed with this strategy, and specially appointed Wang Shao to take charge of the recovery of Hehuang Prefecture. 
The two states of Hehuang were controlled by the Tibetans at that time, which meant that in order to recover the two states, the Northern Song Dynasty had to wage war with the Western Xia and Tubo at the same time, which was strongly opposed by the conservatives led by Sima Guang. They pointed out that Wang Anshi's move was to disturb the Taiping world of the Song Dynasty, but Song Shenzong still chose to support Wang Anshi. This battle lasted for several years, Wang Shao led the army to defeat Tubo, recovered five cities including Hehuang Erzhou, and broke ground for 2,000 miles for the Great Song Dynasty, and Western Xia completely fell into the control of the Song Dynasty. Wang Shao's victory brought Wang's reform to a climax, but it was accompanied by stronger opposition from conservatives, who jointly signed a petition calling for Wang Anshi's dismissal. At this time, Sima Guang, who was outside, wrote three handwritten letters to Wang Anshi. The content of the first letter was to ask Wang Anshi to stop the reform of the law, saying that the reform was to exploit the people and ignore the interests of some **, which completely disrupted the peaceful life of the Song Dynasty. In this regard, Wang Anshi replied, but only a few words. After reading the second letter, Wang Anshi threw it into the stove. Sima Guang, who had not waited for Wang Anshi's reply for a long time, wrote a third letter. This time, Wang Anshi didn't dismantle it, and threw it directly into the stove. At this point, Sima Guang became angry, and the two broke up completely. After the death of Song Shenzong, Zhao Xu, who was not yet ten years old of Song Zhezong, ascended the throne, and the Empress Dowager Gao, who was close to the conservatives, listened to the government, and Sima Guang, who was released, was recalled and served as the prime minister. The Song Dynasty immediately ushered in earth-shaking changes. 
Sima Guang carried out a series of ruthless dimensionality reduction attacks on the reforms, all of which were abolished, and all reformers were demoted or deposed. It can be seen how much Sima Guang hates Wang Anshi's changes. Wang Anshi finally stayed away from the capital and made a small place. The change lasted only fifteen years under Sima Guang's hatred, and it was completely smashed. But Sima Guang still did not understand his hatred, and his eyes were fixed on the territory opened up by Wang Anshi for the Song Dynasty, and he started the imperial court to return all the 2,000 miles of territory opened up that year to Western Xia. Sima Guang pointed out that these territories were snatched from the Western Xia and were ill-gotten gains, which would cause the Western Xia to hold grudges. The return of the territory will definitely bring peace to the Song Dynasty. However, such nonsense is still supported by many conservatives. However, Sima Guang's suggestion was strongly opposed by the feudal officials, who took out the map of the Song Dynasty and questioned Sima Guang, Hehuang Erzhou has been the old land of the Han and Tang dynasties since ancient times, and it is obvious that Tubo and Western Xia have robbed us of our land. Sima Guang was speechless about this, but he still insisted on his claim. In the end, Sima Guang persuaded Empress Dowager Gao to leave only the two states of Hehuang, and the rest of the cities were all returned to Western Xia. When Wang Anshi learned of this news, he also went to the table overnight, explaining the pros and cons, hoping that the emperor would think twice, and there was no claim to return the territory since ancient times. It's a pity that the court at that time was already a conservative world, and his letter could no longer reach the emperor. 
After Sima Guang exterminated the reformers, could his political ideas really bring peace and prosperity to the Song Dynasty?From the first day of the return of the lost lands of the Western Xia, the Western Xia decided that the Northern Song Dynasty was a paper tiger and began to unscrupulously invade the borders of the Song Dynasty, and the Song Dynasty fell into more wars. The annual military salary expenditure of the Great Song Dynasty is innumerable, and it has entered a dangerous realm. But Sima Guang still didn't stop. He valued partisan competition, cultivated his own power, and never forgot to suppress Wang Anshi's old department. His energy was not put on turning the tide for the Song Dynasty and reversing the country's destiny, his hatred for Wang Anshi had reached the point of hopelessness, and he pushed the Song Dynasty step by step into the abyss of destruction. Many historians have pointed out that the Song Dynasty's appointment of Sima Guang as prime minister was the biggest failure. He was one of the culprits who caused the fall of the Song Dynasty, Wang Anshi had just turned the situation of the Song Dynasty into a revival, and was beaten by Sima Guang in a blink of an eye. What he brought to the Great Song Dynasty was not peaceful development, but more trouble. 
Sima Guang is a learned writer and poet, which is true, but he is really not suitable to be a politician, and his appearance in the Song Dynasty is the misfortune of the Song Dynasty.