The July 7 Incident and the Battle of Songhu were not expected by the Japanese military. Japan's invasion of China from Manchukuo and landing from Shanghai was intended to control important cities along the north and southeast coasts and along the river, and to use the resources of north China and southeast coasts to support its subsequent Pacific operations. China is not the ultimate strategic goal of the Japanese cabinet and military ministry, but the stage for achieving its more ambitious strategic goals. Therefore, despite konoe's cabinet's declaration that it would not take the Chiang regime as an opponent, Japan never gave up the "peace talks" with the Chongqing government, and even with Wang Jingwei's puppet government, Japan still repeatedly threw bait at Chiang through Germany.
From a military point of view alone, after the Battle of Wuhan, the Japanese army had every strength to go up the Yangtze River and crush the Chiang Kai-shek government in one fell swoop – from Wuhan to Chongqing, it was not much farther than from Shanghai to Wuhan. After the "Battle of the Continental Lines of Communication" (Battle No. 1) in 1944, the victorious Japanese army occupied most of the provinces of Henan, Hunan, Guangxi, Hubei, guangdong and other provinces, and was also able to take advantage of the victory to pursue and destroy the crumbling Chongqing regime.
But Japan must also consider the development of the war situation politically and economically –what good would it be for Japan if the Chiang Kai-shek regime were eliminated? In the so-called "stalemate" stage in the middle and late period of the War of Resistance Against Japanese Aggression, Japan did not adopt the strategy of "snake swallowing elephants", and even jiangxi, Henan and other areas closer to Jiangsu, Zhejiang or Pingjin were only partially occupied. Japan did not have the will to annex all of China as a colony, and doing so was economically and politically detrimental to Japan. Japan did not get more resources in the barren western part of China, but instead invested its own insufficient resources to maintain these places.
At that time, the western region of China was in difficulty in transportation and could not support the battle of the large corps. The Japanese historian Kazutoshi Hanto noted in the Showa History:
No matter how strong the Japanese army is, supply is always an issue. Since only points and lines can be obtained, as long as the hand is slightly loose, the gap between them is suddenly cut off. Chinese mainland is very deep and wide, even if you only think about supplies, it is a headache. Finally, Hankou was controlled, the so-called end point or tipping point of the attack. In other words, if you attack further, you will fall into an unfavorable state... The reality is that even if many Japanese flags are planted on the vast map of China, if you look closely, only the main cities are occupied, and between the cities and the cities, almost all of them are still enemy land.
Japan has always "left a hand" in its war against China, not that Japan is particularly benevolent to China, but that Japan also has to fight against much more powerful enemies- the United States and the Soviet Union. Comparing the situation at the time of the Ming, Qing, and Yi Dynasties, it is clear at a glance -- after the Eight Banners Entered the Pass from Manchuria, the first army was divided into two routes: one was from Shanxi to Henan to take Tongguan; the other was to go around the outside of Shanxi to northern Shaanxi, defeating the regime of Li Zicheng in Guanzhong, and then going south to Jianghuai, Jingxiang, and Sichuan, eliminating the Southern Ming, and obviously the unified war method.