Duanping's entry into Luo was a strategic attempt by the Song people to regain lost territory since the establishment of the Southern Song Dynasty. After the Jin Dynasty was destroyed, the Southern Song Dynasty launched a northern expedition, hoping to recover the three capitals that had fallen earlier, that is, the three cities of Luoyang, Shangqiu, and Kaifeng. However, for some reason, the Song army that participated in this war broke through the sand and ended in dismal conditions, and in the end, this operation became the fuse for the full-scale outbreak of the Mongolian-Song War.
Some history lovers believe that if the Southern Song Dynasty could send the famous general Meng Jue to command in this war, then the result would be very different. According to historical records, Meng Jue, Shi Songzhi and others believed that there was a world of difference in national strength between Mongolia and the Southern Song Dynasty, and even if this war could be successful, it would not be able to defend against the Mongol counterattack.
Speaking of which, the strategic theory of "duanping into Luo" was first put forward by the Jin people, and this strategic system is similar to the tactic of "refusing to pass the border and guarding the river" formulated by the Jin people in the early years. At that time, the Jin dynasty's power was compressed to the south of the Yellow River, and it could only use a corner of Henan as a base, and successfully blocked the Mongol road south by virtue of natural dangers. Finally, if it were not for Mongolia borrowing from the Southern Song Dynasty, I am afraid that Mongolia would not be able to help the Jin Dynasty for a while. However, when the Jinguo used this tactic, at least 200,000 Jin soldiers were stationed in the Sanfengshan area.
That is to say, if the Southern Song Dynasty wanted to copy this strategy, it would at least deploy 150,000 Song troops before the Yellow River froze in winter. Judging from the declining national strength and inefficient administrative capacity of the Southern Song Dynasty at that time, even if all the troops of the Southern Song Dynasty were drawn out, it would not exceed 150,000. Therefore, the possibility of completing this strategic plan is infinitely close to zero, except for Song Lizong, who does not understand the military, and some crazy main battle factions, the old ministers of the DPRK and China do not agree to implement this tactic.
At that time, entering the Central Plains to regain lost territory, it was mainly possible to march along two strategic routes, namely Huaixi and Xiangyang. The tactic formulated by Song Lizong was to divide the soldiers into two ways. However, when the battle plan was implemented, less than 70,000 Huai troops participated in the operation, and Shi Songzhi and others refused to accept the dispatch and did not respond to the holy will. Although Shi Songzhi's behavior has been criticized by later generations of history lovers, it is very correct to look at Shi Songzhi's approach from the perspective of later generations.
From the Lianghuai region to the Central Plains, there are still rivers that can transport grain. However, if you march from Xiangyang, you will face the dilemma of "having to load twenty hours to cause a stone, and I am afraid that it may not be able to reach it". Since the efficiency of the Xiangyang supply line is terriblely low, it is better to abandon this military operation with a high probability of failure and retain its strength. Unfortunately, Song Lizong did not see the battlefield situation at that time at all, and insisted on sending two generals, Zhao Kui and Quan Zicai, from Huaixi into the Central Plains.
It was a sweltering heat, so most of the Mongol forces were stationed north of the Yellow River, and only some of the Jin who surrendered to the Mongols were stationed in Henan. Therefore, these 60,000 Song troops effortlessly took Fenjing and Shangqiu. After tasting the sweetness of victory, the army into Luo divided into two routes, and the two echelons accelerated their speed towards Luoyang. Because the Mongols had dug the banks of the Yellow River in previous wars, so that the yellow river breach was flooded, and the roads in the Yellow River basin were generally muddy and unsuitable for transportation, the supply lines of the Song army had become a problem at that time.
After the Mongols received the intelligence, they sent a vanguard force to carry out a sneak attack on the town of Longmen outside Luoyang. During this period, the second echelon led by Yang Yi was attacked by The Mongol cavalry due to carelessness and light enemies, and was completely destroyed in only one round.
On another battlefield, the 30,000 Mongol cavalry led by the Mongol commander Tacha'er fought with the first echelon of the Song army, and the battle situation was quite stalemate, "killing more than 400 people, winning more than 300 regimental cards, and not understanding until noon." This also reflects from the side that the Southern Song Dynasty Huai Army still had a certain combat effectiveness during the field battle, and the heavy armored soldiers and crossbowmen were enough to compete with the Mongolian mounted archers.
However, in the Battle of Longmen Town, the second echelon of the Song army was completely destroyed, so the first echelon of the Song army needed to face far more than the Mongol army in front of it, but also a cavalry unit with strong combat effectiveness. What was even more unbearable for the Song army was that the Mongols used the advantage of mobility to block the grain route in an attempt to fight a protracted war with the Song army. In desperation, the Song army had to retreat to the south, but was intercepted by Mongol cavalry halfway through, killing and wounding them.
What was the impact of this war?
After this battle, the Southern Song Dynasty lost nearly 40,000 field troops, and a large amount of grain and grass and military salaries were destroyed and intercepted during transportation, so that the Southern Song Dynasty lost the last bit of family to compete with the Mongols. What is even more frightening is that the Mongolian and Song countries, which originally maintained a delicate relationship, turned their faces because of Song Lizong's initiative to go to war, and the Mongols obtained the excuse of the southern expedition.
Just the following year, the field soldiers alone dispatched more than 100,000 Mongol legions, and naturally launched an all-out offensive against the Southern Song Dynasty, which plunged the Southern Song Dynasty into a situation of no return. From here, we can see that the launch of this war was a mistake, and the ignorance of the main war factions such as Song Lizong made the Southern Song Dynasty give up its last vitality.
It was also because of this war that Song Lizong's attitude toward the outside world underwent a major change. Duanping's defeat dealt him a heavy blow, and the enthusiasm that had previously been high was in vain, and was replaced by passive conservatism, which continued throughout the government that followed him. Although Emperor Xiaozong of Song lost the Longxing Northern Expedition, he and Yu Yunwen never forgot to recover the Central Plains, and they also made great achievements in governing internal affairs. Song Lizong did not raise his spirits after this setback, and the seeds of the demise of the Southern Song Dynasty, such as the death of Yu Jiu and the rebellion of Liu Zhen, were planted in the later period of Song Lizong's reign.
Resources:
[History of Song Vol. 417, Liechuan 176, Qi Dongye Language, Vol. 5]