Why is the capital of War of Resistance against Japanese Aggression Chongqing instead of Chengdu?

During the War of Resistance against Japanese Aggression period, under the crazy attack of Japanese invaders, Nanjing, China fell. At that time, the Kuomintang Central Committee had to give up Nanjing and move to Chongqing. But the problem is that the middle of Shu is vast, and Chengdu is the best choice for retreating to Sichuan in the past dynasties. For example, after Shu Han won Yizhou, he chose Chengdu as the capital to fight against Cao Wei, and Tang Xuanzong also chose Chengdu as a temporary refuge during the Anshi Rebellion. So why did Chiang Kai-shek give up Chengdu and choose Chongqing as the capital? In fact, there are three main reasons:

First, Chongqing is a mountain city. Compared with a Ma Pingchuan in Chengdu, Chongqing is more stereoscopic and easier for air defense. In the cold weapon era, broadsword and spear were the main weapons, and the fighting style was flexible flat cable-like. Defenders on the Chengdu Plain need not worry about the enemy falling from the sky. On the contrary, vast land can support a large number of people. However, modern warfare is three-dimensional, three-dimensional. In this case, Chongqing has reduced the bomb area compared with Chengdu. Moreover, Chongqing is almost surrounded by mountains, which can make up for the shortage of China's air superiority. Under the historical conditions at that time, only Chongqing could resist Japan's strategic bombing for five and a half years.

Secondly, from a geographical point of view, Chongqing is the gateway to the Sichuan basin, guarding the Three Gorges of the Yangtze River and taking Daba Mountain as a natural barrier, which makes it impossible for the Japanese mechanized army to attack Sichuan and the navy to go upstream, which Chengdu does not have. Since the Japanese invasion of China, it has been advancing from North China and East China to the core area of China. After the fall of Nanking, a great deal of materials and munitions from China were transported westward along the Yangtze River waterway. At this time, Wuhan, because there is no danger to defend, is extremely vulnerable to the impact of the Japanese army along the Pinghan Railway and can only be transported westward to Chongqing. The biggest difference between Chongqing and Chengdu lies in the perfection of transportation facilities. To be fair, before the outbreak of War of Resistance against Japanese Aggression, local warlords in Sichuan had made great efforts in infrastructure construction in Chongqing, so Chongqing's function as a city was more perfect than that of Chengdu. At this time, there is no railway between Chengdu and Chongqing, so it is simply unrealistic to transport materials from Chongqing to Chengdu.