Japan Invades China — Second Sino-Japanese War Begins

A skirmish at the Marco Polo Bridge near Beijing provided Japan's pretext for a full-scale invasion of China, beginning eight years of brutal warfare that killed 15–20 million people. Japan quickly captured Beijing, Shanghai, and Nanjing, with Chinese Nationalist forces under Chiang Kai-shek retreating inland. The war merged with the global WWII conflict after Pearl Harbor but had effectively been underway since 1937, making China the longest-fighting Allied power.