By the early twentieth century, Japan was in the throes of rapid industrialization. Because of the limited natural resources available on the Japanese archipelago, industrialization meant expansionism. To this end, Japan had expanded its military and political influence in Manchuria and Korea. Expansion in the former led to conflict with Russia, and Japan won a staggering victory over the Russian Empire in 1905. Manchuria became a Japanese province (as had Korea) in 1931. The point is that Japan had risen as a military power long before World War II, because military conquest was deemed essential to Japan's economic well-being.
With these developments, militarists became increasingly influential in Japanese government. In many ways, their tactics were similar to those of European fascists. They murdered rivals (including the prime minister, purged anti-militarists from government influence, espoused an aggressive expansionism, and asserted the racial superiority of Japanese people. But they were also able to exploit an old warrior ethos in Japan, one which placed obedience to the emperor as among the highest of callings. The military leader who assumed the reins of de facto leadership in Japan with the outbreak of World War II was Hideki Tojo.