Emperor Chai Rong of Zhou shizong once tried to retake Yanyun Sixteen Prefectures during the Northern Expedition in the first month of the sixth year of Xiande (959 AD), and his expedition was very smooth: it took only 42 days to recover the seventeen counties of The Three Prefectures. Just as Chai Rong was preparing to attack the northern town of Youzhou, he unfortunately fell seriously ill and had to return to the dynasty.
Later generations therefore believed that Chai Rong advocated "first the north and then the south", that is, to first recover the Sixteen Prefectures of Yanyun, and then to unify the Forces of Later Shu and Southern Tang to the south. But this argument is untenable, because Chai Rong followed Wang Pu's advice shortly after taking the throne and decided to send troops south first.
At that time, Sejong was on the throne, determined to conquer, had already scratched the crowd's opinions, personally defeated Liu Min at Gaoping, returned to Yizhi soldiers, and had the ambition to make peace for a day... At that time, the scribes did not want to rush to use force, in order to quell the rebellion, and thought that xiu wende was the first. However, the Hanlin scholar Tao Gu Douyi, the imperial historian Yang Zhaojian and (Wang) Park all said that the strategy of using soldiers, Park said that Jiang Huai was the first to take. SejongYa knew that Pu was very good, and when he saw that his discussion was great, he was surprised, and he led and discussed the affairs of the world, and there was no disagreement, so he decided to use it.
The above article is from the "New History of the Five Dynasties", and it is clear that Zhou Shizong Chai Rong did not advocate the first solution to the Khitan problem in the north, he advocated "peace in the world" by force rather than "repairing Wende" first. As for whether to go south first and then north or north and then south, Zhou Shizong Chai Rong listened to Wang Pu's suggestion and decided to take Jianghuai first, that is, first south and then north. After Zhao Kuangyin established the Song Dynasty, he and Zhao Pu and others "made a decision on snowy nights", in fact, they still followed the established policy formulated by Zhou Shizong Chai Rong and Wang Pu.
When Zhou Shizong became emperor, the world was continuing to last for a hundred years of war, the people's livelihood was withering, and although the Later Zhou Dynasty was a relatively powerful regime during the Five Dynasties and Ten Kingdoms period, its strength was completely unable to compete with the northern superpower Khitan, so it was necessary to develop its own strength first. In times of war, the most direct and effective way to develop oneself is to use force to directly seize from other regions. The southern states occupied Sichuan, Liangguang, and the middle and lower reaches of the Yangtze River, which had long been one of China's most prosperous regions: there were fewer wars, the economy was developed, and more importantly, the long period of unarmament, which was the primary reason why troops should be used south first.
Therefore, after the strategy of "first south and then north" was formulated, Chai Rong immediately put it into action--soon after he took the throne, he first used troops against Later Shu, and then marched on Southern Tang three times, but Southern Tang had contacted the Khitan and prepared to form a north-south attack on Later Zhou, so that Zhou Shizong Chai Rong was forced to withdraw and attack the Khitan to the north, which led to the six-year Northern Expedition War of Xiande. But Chai Rong died of illness on this way, and we can imagine that if he had not died young, he might have continued to go south and then north, after all, the southern Houshu, southern Tang, Wuyue, Southern Han, and so on are all small treasuries!
Therefore, we can regard Chai Rong's Northern Expedition as an episode in his strategy of "first south and then north", but he unfortunately died of illness in the process of the Northern Expedition, and did not achieve the expected results of the Northern Expedition, let alone complete the unification of the South.
In addition, because of the success of Chai Rong's Northern Expedition and his untimely death, it is believed that he is the most promising person to recover Yanyun Sixteen Prefectures, and this statement does not hold water. The first is the disparity in power between the Later Zhou and the Khitans, which have been developing steadily for decades and have a strong economic and military foundation, while the Later Zhou Dynasty has been in a state of war for many years, and there is no respite at all. Secondly, although Chai Rong's Northern Expedition was smooth, he did not confront the main Khitan forces, and if a direct conflict broke out between the two countries in the later Zhou And khitans, it was really unknown who would win and who would lose.