Since the Tang Dynasty, Japan has launched four wars against China, namely the Battle of Baijiangkou in 663 AD, the Korean War of 15.92 Million Calendar, the Sino-Japanese War in 1894, and the War of Resistance Against Japanese Aggression in 1931.
In 1840, the Opium War began, opening the course of China's modern history, and the British opened the prelude to the invasion of China. The two Opium Wars that broke out in 1840 and 1856 brought reflection to China was the Western Affairs Movement, Li Hongzhang, Zuo Zongtang and others carried out foreign affairs and learned from modern Western weapons and equipment, while Japan at the same time, after being invaded by the great powers, they carried out a top-down reform, and the political, economic, military, educational and other aspects were vigorously innovated, known in history as the "Meiji Restoration".
Then they made a bet-like decision - to take up the knife of war and slaughter China, Japan won the bet, and the defeat of China in the Sino-Japanese War also meant the bankruptcy of the foreign affairs movement, and China's last hope of turning around was shattered, and Japan ushered in the opportunity to surpass China for the first time in thousands of years. In the decades that followed, China was full of Japanese shadows. They began to infiltrate China step by step: occupying Shandong and Cutting Jiaozhou, they read the treaty wantonly and maliciously, and committed one fact after another of encroaching on Chinese territory.
In 1912, the Qing Dynasty collapsed and the Republic of China government entered the political arena. After World War I, foreign powers were still eyeing China and staring at this large piece of fat. At such a desperate and helpless time, the United States stood up, recognized the Republic of China, used Gengzi's reparations to found Yenching University, and said at the League of Nations conference: Japan will not want to annex an inch of China's land.
If you think that the United States is the savior, then you are wrong, in fact, the United States is also unprofitable, it has the same ambitions as Japan, all the United States does is to worry about its own interests being infringed, at that time Asia was a land without hegemony, Britain, France, the United States and other countries in Asia have colonies and interests, and China is a huge market shared by these countries. However, Japan's invasion upset this balance and led to serious losses to the interests of these countries.