The effect of the military development efforts associated with the Meiji Restoration were realized in the first Sino-Japanese War (1894–1895). Victory over China ceded Japan the island of Taiwan and established Japan as a regional power. That status was solidified during the Russo-Japanese War (1904–1905) fought over rival imperial ambitions in Manchuria and the Korean Empire. Japan’s victory shocked the West and solidified its status as a major military power – and especially as a naval power with the utter defeat of the Russian fleet at the Battle of Tsushima – a battle that would shape Japan’s own war planning. 

In 1910 Japan formally annexed Korea. A few years later, Japan was technically a member of the World War I allied alliance against Germany. Japan’s military, taking advantage of the great distances and Imperial Germany’s preoccupation with the war in Europe, seized German possessions in the Pacific (Micronesian islands) and German holdings in China, but there was no large-scale mobilization of the economy needed to support their ambitions. Politically, the Japanese Empire seized the opportunity to expand its sphere of influence in China, and to gain recognition as a great power in postwar geopolitics.

In 1931 the Japanese armed forces (the Kwantung Army) staged an explosion on the South Manchurian Railway as a pretext for invasion. This became known as the Manchurian Incident leading to the invasion and occupation of all of Manchuria. Condemned by the League of Nations, Japan withdrew from the League in 1933.

In 1937 the Second Sino-Japanese War (1937) began. This was a full-scale invasion as Japan captured major Chinese cities (e.g., Nanjing, Shanghai). One effect of this was the need for Japan to push further into Southeast Asia to cut Chinese supply lines. This war is marked by a savagery against civilian populations, especially the Chinese. The notion of nihonjinron (theories of Japanese uniqueness) underpinned broader societal views that placed Japan at the center of Asia and devalued neighboring peoples. Historian Daqing Yang notes that many in Japan, including civilians and intellectuals, viewed the Chinese as a “lesser race” and that this perception was amplified through state propaganda during the Second Sino-Japanese War 

The Rape of Nanjing (December 1937 – January 1938) revealed a deeply entrenched and violent disregard within the Japanese Imperial Army for civilian life in conquered territories. The atrocities committed during this period—mass executions, systematic rape, looting, and arson—were not isolated acts of rogue soldiers but symptomatic of broader attitudes rooted in military indoctrination and racial ideology. Scholarship on the subject suggests that these attitudes reflected not only the values of the military but also prevailing beliefs in Japanese society about cultural superiority and imperial destiny.

Meanwhile, in 1936 Japan withdrew from the Washington Naval Treaty. From this point military spending surged resulting in the aggressive expansion of the Navy, naval air forces and the army. In 1940, Japan joined the Axis powers of Germany and Italy. In 1941, it occupied French Indochina, threatening British Malaya and Dutch East Indies—key sources of oil and rubber.

In July 1941 the U.S., Britain, and the Netherlands responded with embargoes, especially oil, crucial for Japan. Japan imported some 80% of its oil from the United States. Facing economic strangulation, Japanese leaders opted for war to secure resources.

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Image credit: various photographs from Naval Aviation Museum, National World War II Museum, and US Navy Archives.