The emperor's symbolic status in the nation.

The constitution and its regulation of the army:

The Meiji leaders' concern to avoid having the army meddle with parliamentary procedures and therefore leaving the army and navy outside of parliamentary control.

Democratic movements in the 1920s and 35 incidents of lese majeste from 1921-27 led to the crown’s reliance on Nichiren, a Buddhist denomination that was anti-democratic and anti-Socialist. Many of its ultra-nationalistic members became military officers. 

The army’s growing dissatisfaction and assertion of the supreme command, the emperor, as a way to avoid compliance with the 1922 naval treaty.

Tacitly endorsing an expansionist policy, Hirohito fired PM Tanaka who had initially wanted to investigate the assassination of Zhang Zuolin, the Chinese warlord in Manchuria.

This sent a message to the Japanese army in China that they could do as they wanted.