Saying that “World War II began in 1939” leads us to another problem, however: it ignores what was happening outside of Europe.
In fact, by the time Hitler’s Panzers rolled into Poland, the world was already in flames, and had been for years. Africa had seen one of the largest and deadliest colonial wars of all time in 1935-36: Italy’s conquest of Ethiopia (Abyssinia). It featured (at least on the Italian side) tanks, poison gas, and the unrestrained bombing of defenseless civilians from the air; in all ways it was a suitable curtain-raiser on the war to come. In Asia, Japan had been on the march for years, seizing the rich Chinese province of Manchuria in 1931, thumbing its nose at international protests, lopping off Chinese border territories like Rehe (Jehol) in 1933, and, finally, in July 1937, launching a full-scale invasion of China proper. You can’t accuse the Japanese of thinking small: this campaign aimed at nothing less than the conquest of the world’s most populous nation. The Imperial Japanese Army managed to overrun much of north China against the indifferently armed and led Chinese, then linked up with amphibious forces landing at Shanghai in August. The invasion’s signal moment was the orgy of violence after the capture of the capital city of Nanking in December, where the victorious invaders butchered hundreds of thousands of Chinese civilians, apparently just to show that they could. Japan never formally declared war, however, and so this incredibly brutal campaign went by one of the all time understatements: it was the “China incident.”
Surprisingly, given that fast start, China would turn into a quagmire for the Japanese. The regime of Chiang Kai-shek continued to resist the invaders, fleeing to the interior and setting up a new capital at Chungking. Chiang also suspended his long-running civil war with the Chinese Communists under Mao Tse-tung in favor of a United Front against the Japanese. Foreign supplies also began to flow into China, with arms from the U.S. and Great Britain arriving via a new “Burma Road” hacked out of the mountains. American pilots came to China as mercenaries, flying as the American Volunteer Group and helping to contest Japanese control of the air. As a result, by 1941, the fighting had stalemated. Large chunks of China were in Japanese hands, but even with a troop commitment of some 1.5 million men, Japan was no closer to ultimate victory. It couldn’t win in China, nor could it simply cut its losses and go home. It ultimately decided to solve that problem by dramatically widening the war, conquering an empire in Southeast Asia and the Pacific, regions rich in tin and oil and rubber, so that it could bring its war in China to a successful conclusion. The “China Incident,” in other words, led directly to Pearl Harbor.
My take: 1937 is as good a date as any to use for the start of World War II.