I disagree with that best answer. A lot of things are not right.
1, can't rely entirely on military commanders. In fact, there were many upright and patriotic generals in the Song Dynasty. The most fundamental problem is the concept of governing the country in the Song Dynasty, which emphasizes literature over martial arts and emphasizes internal affairs over external affairs. It turned out that there were some horse-producing places in the northwest of Song Dynasty, but they were lost because of the rise of Xixia. I also had a horse strategy, but it was better. I got it for Emperor Song. It turned out that there was an elite cavalry, the Static Serbian Army, which was also defeated by the monarch and his subjects in the Song Dynasty. The military system of the Song Dynasty, under this idea of governing the country, was also deformed, with strong cadres and weak branches. The most elite soldiers guarded the palace gate for the emperor, while the relatively scum soldiers were kept in the border town. Such an army, even a natural general, is hard to win. Emperor Song also liked to send laity to interfere and command blindly. Since Song Taizong in the Song Dynasty, emperors were weak, proficient in calligraphy, not good at military affairs, and lacked the overall situation, which led to many political mistakes. The Song Dynasty was rich in materials, which also eroded people's enterprising spirit. The emperor paid no attention to the army, and soldiers had no sense of honor. Many people join the army just to stutter. One emperor needs special mention here, and that is Song Renzong. Many of his practices are soft on women, causing endless harm. In order to reduce the unemployment rate, a large number of soldiers were recruited to support the people. However, the financial pressure is too great. How can we make up the financial resources? Letting the army do business will inevitably lead to corruption, fear of death and a decline in combat effectiveness.
2. The problem of lack of horses has been puzzling the Central Plains Dynasty, but there were still a large number of horses in the Han and Tang Dynasties, mainly in the north, and many excellent horse breeds were introduced. The Song Dynasty was congenitally deficient, and there were no sixteen states with hidden clouds. Not only is there no obstacle, but there is also a lack of excellent pasture. The Silk Road was blocked by Liao, so it was difficult to import excellent horse breeds from the western regions. But there was no shortage of horses in the Song Dynasty, what was lacking was excellent war horses. A war horse has a high standard. Must be as high as possible, run fast, be resistant to rough feeding, not easy to get sick, have no accidents, and have strong endurance. Since ancient times, the Central Plains has not produced good horses, lacked excellent pastures, and lacked people who are good at cultivating good horses. Although the Song Dynasty engaged in horse administration and raised hundreds of thousands of horses, there were more horses than horses. A slight improvement was ruined by Sima Guang and a group of pedants. To cultivate excellent war horses, we should not only have excellent horse breeds, but also have a suitable environment, such as the hot and humid environment in the south, which is prone to horse plague. Moreover, without large open space to build pastures, horses cannot run often, so their running ability will not be trained quickly. This is also geographical determinism. Since ancient times, the good horses in China are basically in the northwest or northeast, and the good horses in North China are also dystocia, and the horses get shorter and worse as they go south. Outside the Great Wall, although the environment is harsh, it is a natural pasture. Those nomads, every family keeps horses, and every family has dozens of horses. Moreover, the variety of horses is excellent, cold-resistant and heat-resistant, good at running, resistant to rough feeding and free of forage. In the Song Dynasty, the cost of raising horses was high, and the number of war horses was less than that of prairie people, which was a disadvantage. Many people don't know how terrible the war consumes horses. In the early stage, Emperor Wu of the Han Dynasty relied on more than 700,000 military forces in the country, and the treasury had enough money and food to severely crack down on the Xiongnu. In the later period, it became more and more insufficient, because the number of war horses could not keep up with consumption, and a large number of horses were needed for transportation. A large number of horses were frozen to death, shot or slaughtered for food. There are millions of horses on the grassland, and the grassland is suitable for raising horses. It is much healthier and grows faster, so it is not easy to get sick. Mongolian horses can chew some grass and drink some horse milk when they are hungry. This logistical advantage is really incomparable to the Central Plains Dynasty.
Song dynasty didn't buy horses from foreign countries. The Song Dynasty not only bought horses from Liao and Xixia, but later both Liao and Xixia found it dangerous to lose so many horses, so they stopped exporting horses to the Song Dynasty. In the Song Dynasty, Ryukyu imported only a few hundred horses a year, which was a drop in the bucket. After the Jin people invaded the south and lost to the north, Jurchen would not sell horses to the Song Dynasty. The Southern Song Dynasty could only buy horses from Tubo. Tubo horses are expensive, but not as good as Mongolian horses, and the number is small, so it is difficult to transport on mountain roads. This is also the fundamental reason for the lack of powerful cavalry units in the Song Dynasty. Moreover, the horses in the whole Song Dynasty were basically used for war, and the horses in Liao, Xia and Fan were basically consumed on the battlefield, which led to the fact that horses were rarely used by the people, and more cattle and donkeys were used to pull carts. As for importing horses from Arabia and India, I can only say that you are naive and always habitually ignore the cost performance. Ocean transportation, long distance, bad sea conditions, stuffy cabin, it is good that one tenth of the horses can survive. Even if there is, it cannot be imported in large quantities. I really can't afford tens of thousands of war horses in the Song Dynasty.
When it comes to corruption, there are actually civil and military officials. In the final analysis, it was caused by the concept of governing the country and political problems in the Song Dynasty. The Song Dynasty was rich, developed in economy and culture, and advanced in science and technology, but it rarely invested these in strengthening the army. However, the rulers of the Song Dynasty gave generous treatment to officials, but there was no good supervision mechanism. The interests of military commanders, their consorts and bureaucratic groups in the Song Dynasty are intertwined at different levels and complicated. In the final analysis, it was the high-level officials in the Song Dynasty who ignored the fundamental problems because of long-term stability. Only a few reforms ended in failure. In the Southern Song Dynasty, the problem of warlords became more and more serious, and it was common to eat empty salaries.