Final answer:
Militarist leaders in Japan rose to power in the early 1930s primarily due to their successful invasion of Manchuria which showcased their military strength and the civilian government's diplomatic ineffectiveness, coupled with their anti-Communist ideology and fears of Communism's spread in Asia.
Step-by-step explanation:
Militarist leaders gained control of the Japanese government in the early 1930s due to several factors. The invasion of resource-rich Manchuria in 1931 was a significant factor. This incident highlighted the Japanese military's capability and the civilian government's diplomatic failures, which further empowered the radical military leaders. Additionally, the Japanese military justified their actions as liberating Asia from European colonialism, and they saw an opportunity to expand their territory due to the turmoil in China and the fear of Communism spreading in Asia. Japan's alignment with anti-Communist sentiment resonated with the ideologies of Fascism and National Socialism, leading to the Anti-Comintern Pact with Germany in 1936.
Operating with a heightened sense of duty and contempt for civilian leaders, the military establishment led by highly nationalistic and imperial-minded individuals took control of the government, advocating for an expanded Japanese Empire similar to European imperial powers. These political shifts were heavily influenced by Japan's need for resources to sustain its industry and to potentially establish a dominant presence in East Asia, as part of their vision for the "Greater East Asian Co-Prosperity Sphere". The military's rise to power was not due to a civil war in Japan, Hideki Tojo's appointment (which happened later), or U.S. shipments to China, but rather their own imperial ambitions and successful military ventures.