The fundamental reason why Japan launched a war of aggression against China?

According to the established national policy, Japan determined the armed aggression policy of "conquering Manchuria and Mongolia" at the 1927 Eastern Conference: "If you want to conquer China, you must first conquer Manchuria and Mongolia. If you want to conquer the world, you must first conquer China."

This policy comes from "The Empire's Positive Fundamental Policy towards Manchuria and Mongolia". It is said that the patriot Cai Zhikan took advantage of his connections with the Japanese political party and risked his life to sneak into the imperial library in the Japanese Imperial Palace and use It took two nights to transcribe it and publish it in China.

Extended information:

After 1927, Japan followed the policy of armed aggression and launched its encroaching aggression against China step by step.

On September 18, 1931, the Japanese Kwantung Army used an excuse to attack Beida Camp in Shenyang, creating the "September 18th" incident that shocked China and foreign countries.

In March 1932, Japan supported Puyi, the deposed emperor of the Qing Dynasty, and established the puppet "Manchukuo". The three eastern provinces were completely reduced to Japanese colonies.

With the connivance of Chiang Kai-shek's non-resistance policy, he brazenly dispatched troops in early 1933 and continued to launch a large-scale offensive into the North China region within the pass.

On January 4, 1933, the Japanese vanguard force of more than a hundred people occupied Chengde City, the capital of Jehol Province, without a single blow or a shot.

Then, the Japanese army divided its troops into several groups to attack each entrance of the Great Wall. After occupying seven counties including Duolun and Zhangbei in the eastern part of Chahar, it approached Tongzhou, Beiping (today's Beijing) and Tianjin in May.

Japan’s plan to conquer Manchuria and Mongolia was almost fully realized. Japanese and puppet regimes were established in Inner Mongolia and Northeast China one after another. The Chinese nation was in extreme danger.

Reference: Baidu Encyclopedia-Tanaka Memorial