[2] However, Uesugi's views began to change during his stay in Europe from 1906 to 1909, where he studied under Georg Jellinek at the University of Heidelberg.

[3] Beginning in 1911, following his return to Japan, Uesugi launched a sustained series of attacks against Minobe's Emperor Organ Theory, which up until that time held broad, mainstream acceptance.

[4] In these attacks, Uesugi accused Minobe of violating Japan's sacred kokutai ("national essence") by arguing that the Japanese Emperor was subordinate to the state.

In 1913, Uesugi formed a group called the Tokagakkai ("Paulownia Flower Society") to defend the kokutai against Minobe’s Emperor Organ Theory and to work for the eradication of all political parties.

[1] In his role as a professor of law at the elite Tokyo Imperial University, Uesugi also trained and mentored many notable right-wing politicians and political activists who were students of his, including future prime ministers Nobusuke Kishi,[6][7] Eisaku Satō,[8] and Takeo Fukuda,[9] and political philosopher Masahiro Yasuoka.