Tell the truest history in the simplest words.
After formulating the unification steps of the south first and then the north, Zhao Kuangyin, the grandfather of the Song Dynasty, did not stop his unification pace for a moment in order to realize his ambitions. Although jiangnan's national strength had declined at that time, after all, the Southern Tang Was the most powerful country in the Ten Kingdoms. Therefore, for the Southern Tang, Zhao Kuangyin has been making preparations. Zhao Kuangyin's goal was very clear: to destroy the Southern Tang.
Song Taizu
Although, Zhao Kuangyin's yellow robe was added to his back, the land was vast, the military expenditure was sufficient, and the number of soldiers was tens of thousands. Although Zhao Kuangyin had enough capital to destroy the Southern Tang, the clearest thing for a person to do things should not be what he wanted to do, but more importantly, he also had to know what he was afraid of and what he lacked.
Zhao Kuangyin was afraid of something that was almost universally known. He was most afraid that the rights he had so hard to get would be lost from his hands. So he has to "think twice before doing anything big." The Southern Tang had an opponent that made Zhao Kuangyin afraid: Lin Renzhao. This person had a prestige, a practical combat experience, a third, wisdom and courage, and more importantly, in the Southern Tang Dynasty, his influence was higher than that of Li Yu, the lord of jiangnan. Therefore, Zhao Kuangyin had to consider the great enemy of the Southern Tang Dynasty.
Li yu
In addition, he was also worried about being caught between the north and the south. Therefore, before sending troops, it was urgent for Zhao Kuangyin to solve the rear pressure (Khitan). Although Zhao Kuangyin later stirred up dissension, causing Li Yu to poison Lin Renzhao and intermarry with the Khitan to resolve the rear contradictions, this was all an afterthought.
Zhao Kuangyin was more aware of what he lacked.
The first is the water shortage army. The Great Song Dynasty stood in the Central Plains, and the army and cavalry were the strongest in the Great Song Army; the Southern Tang Was located in the south of the Yangtze River, with hills and rivers and lakes weaving, and had a powerful water army. And if he wanted to send troops to the Southern Tang, water combat was inevitable. What he lacks most is a "water force" that can resist the "Jiangnan Water Army".
In order to build a water lion as soon as possible, Song Taizu "fortunately built a ship to observe water warfare," and twice in a row, once "Jianlong two years" and once "Jianlong three years", which shows the urgency of Zhao Kuangyin's heart.
The second is the lack of a map, a map of the Southern Tang Dynasty. The so-called "knowing oneself and knowing the other will never be lost in a hundred battles," Zhao Kuangyin urgently needed to figure out the maps of the mountains and rivers in Jiangnan, the distribution of cities and pools, and the dispersion of the population, which naturally did not need to be too worried about Song Taizu, because he had ordered Hanlin student Lu Doxun to stay in the Southern Tang and draw a map of the Southern Tang.
The third is the lack of a bridge. Zhao Kuangyin's army set out from the Central Plains and needed to cross the mighty Yangtze River in order to capture Jinling, the capital of the Southern Tang Dynasty. In order for the main army of the Great Song Dynasty to cross the Yangtze River smoothly, it is necessary to have the "Yangtze River Bridge." "This bridge does not need Song Taizu to worry too much, someone dedicated it to him."
This person is Fan Ruoshui, a native of Jiangnan. The reason why he defected to Zhao Kuangyin was that, simply put, he was depressed in the Southern Tang Dynasty. Since ancient times, when the scholars were discouraged, whoever had an olive branch would fly wherever they went. Zhao Kuangyin threw an olive branch, "Yangtze River Bridge". Fan Ruoshui had already begun to prepare in order to defect to Zhao Kuangyin.
Fourth, most importantly, he lacked a reason to attack the Southern Tang. Although there is no excuse for the sin of wanting to add, it is better than not, and it is not difficult to find a suitable name. The history books say: "Some of the generals have been put on the top, but there is no name for the master." This means that Zhao Kuangyin sent various generals to set off, but they had not yet found the name of the conquest.
So how did Song Taizu attack the Southern Tang in the right name?
In 974, the Great Song sent envoys to Jiangnan, and the envoys asked Li Yu, the lord of Jiangnan: "The imperial court now has a great gift of firewood to sacrifice the heavens, why doesn't the lord of the country come to help the sacrifice?" "The lord of the country only does not answer", Li Yu did not answer, which gave Zhao Kuangyin an excuse to send troops to "refuse the DYNASTY".
Up to this point, Zhao Kuangyin had two fears and four deficiencies. But Song Taizu strategized and prepared for the rainy day, dealt with all the "two fears and four deficiencies", and realized his ambitions!
References: Volumes 2, 3, and 15 of the Continuation of zizhi Tongjianchang; The Biography of Lin Renzhao of the Southern Tang Dynasty