The Attaché

Juria Katakawa | Originally Published: 3 May 2026

On May 15th, 1932, a group of Japanese right-wing naval officers masterminded the assassination of Prime Minister Inukai Tsuyoshi in an attempted coup d’état. Nonetheless, the longest sentence imposed by the court on the culprits of this “terrorist act” was a mere fifteen years (The Office of the Historian 1993, 771). Historians can only blame nationalism for cultivating a culture of political violence in Imperial Japan. This inherent nationalist sentiment inspired solidarity among the masses who antagonised the restrictive Western powers, while ironically threatening the valuable lives of the Japanese community at the same time. Accordingly, this paper will explore the question: how did the May 15th Incident (1932) foster Japanese nationalism and the rise of hardline militaristic leaders, ultimately motivating Imperial Japan’s expansionist foreign policy in the Far East? Japanese nationalism in the 1930s served as both a cause and effect of the assassination of Prime Minister Inukai, which was a violent condemnation of Inukai’s acceptance of the Western powers’ limits on Japanese military strength. When a hardline militaristic administration replaced its liberal predecessor and implemented nationalist domestic and foreign policies, Imperial Japan was set on a path towards unconstrained expansion in mainland China. 

The Incident’s Impact on Japanese Popular Nationalism

Although the coup d’état failed in its immediate aims, Japan’s naval officers were successful in creating lasting effects of developing nationalist sentiment. The defendants framed their crime as an expression of devotion to Imperial Japan’s self-sufficient aims. In Imagined Communities, Benedict Anderson defines nationalism as the devotion to an imagined, political community (Anderson 2016, 4). This sense of fraternity takes the form of a bottom-up, “popular nationalism” in Imperial Japan (30). When the common people became dissatisfied with the ruling government, they emphasised the need for the rebirth of the nation. In their courtroom defence, Inukai’s assassins embarked upon lengthy diatribes alleging that their victim had “weakened” the nation (Huffman 2010, 222). Among the plethora of socio-economic issues looming in Japan at that time, the right-wing officers were particularly angry at Inukai’s refusal to recognise the independence of Manchukuo, a puppet state created by the Empire of Japan (Byas 2011, 20). This resentment against the Prime Minister allowed for the moral reconstruction of the ruthless murder into an ethically valid and even necessary action in the eyes of the defendants. The development of Japanese nationalism included the belief that Japan urgently needed a radical “renovation”, which would only be possible with the elimination of “evil elites”, including Inukai (33). The young naval officers painted Inukai as a burden to Japan’s prosperity, necessitating their crime in the name of popular nationalist rhetoric.

Mass media amplified these nationalist views by reporting the defendants’ statements compassionately, increasingly influencing Japanese citizens in the process. Anderson argues that nationalist sentiment promoted through print capitalism united various social classes in the early examples of nation-building (2016, 31). In the context of interwar Japan, newspapers and radios had a similar function in echoing nationalist rhetoric, such as that of Inukai’s assassins. In response, the court trying the Prime Minister’s murder received over 100,000 letters appealing for the defendants’ mercy, many of which were written in blood (Byas 2011, 30). The assassins’ testimonies evoked considerable sympathy outside of court and within, especially in the military. News spread to motivate nationalist organizations, including the Teikoku Zaigo Gunjinkai (the Imperial Military Reserve Association), to rally outside the courthouse and at Shinto shrines to support the accused (Large 2001, 564). General Araki, leader of the ultranationalist Kōdō-ha faction, summarised this societal justification of the criminal acts: the “pure and naive young men” merely “performed in the sincere belief that they were for the benefit” of the nation (Maruyama and Morris 1969, 67). The role of mass media in rapidly spreading nationalist sentiments of Inukai’s assassins replicates Anderson’s theory on print-capitalism.

After the May 15th Incident, the liquidation of liberal politicians was socially and morally acceptable for the sake of securing the nation’s interests. Nationalist public opinion pressured the court to sentence most of the defendants to only four years (Maruyama and Morris 1969, 68). This legal decision was a reflection of the nationalists’ substantial influence in Japan, since the very system meant to ensure a peaceful and just society tolerated the naval officers’ barbaric crime. The American Ambassador to Japan at that time, Joseph C. Grew reported that the defendants even threatened to continue to take “direct action” to “bring the nation to its senses” (The Office of the Historian 1993, 2). Rather than an avenue to bring criminals to justice, the murder trial became a platform to spread nationalistic feelings to the public and undermine the democratic government. The trial of Inukai’s killing allowed radical nationalism to flourish in interwar Japan at the cost of the lives of liberal leaders and judicial values.

The Political Significance of the May 15th Incident

While this paper focuses on Inukai’s assassination, this case took place in a larger Japanese culture of political violence in the 1930s. In the first half of the decade, the Japanese government was victim to twenty terrorist incidents, four attempted coups, and four political assassinations (Maruyama and Morris 1969, 69). Notably, the assassination of Prime Minister Hamaguchi two years before Inukai was similarly motivated by resentment towards Hamaguchi’s liberal reforms and his signature on the London Naval Treaty (Fleisher 1930). The assassin was a member of the Aikokusha, a reactionary organisation that regarded the Treaty as a “menace to imperial defence” (Fleisher 1930). The murders of the two prime ministers responsible for the Treaty reflects Japanese society’s overall anti-government sentiment. Moreover, Korekiyo Takahashi, the finance minister known for negotiating the Washington Naval Treaty in 1922 with the US and Great Britain, was killed in the February 26 Incident (1936). The intensely nationalistic elements dissatisfied with Japan’s relatively smaller naval vessel ratio conspired to assassinate the “betrayer” (The New York Times 1936). Political violence was a prevalent motif in Japan in the 1930s because the criminal acts punished leaders who strayed from military approaches to governance.

Among these examples of political violence, the May 15th Incident was a distinct case because it ended the system of party cabinets. Much of the literature on prewar Japan uses the consolidation of the Nazi’s one-power system in Germany as an analogy for Inukai’s assassination. Even more abundant is the language marking Inukai’s death as the end of civilian political control over government decisions, at least until the revocation of the Meiji constitutional order (Huffman 2010, 52). Inukai’s assassination led to high political tensions, where the general population perceived the democratic pirates as weak, and ultranationalist groups threatened further acts of violence (Huffman 2010, 57). Without the confidence of the electorate, democracy in Japan was doomed to be at the hands of a burgeoning militarism. Overwhelmed by these nationalist sentiments, Prince Saionji was forced to put an end to the party government (Siniawer 2011, 1002). Henceforth, Japan was governed by national unity cabinets where eight of the eleven prime ministers in the following decade were all generals or admirals, each seemingly more hardline than the last (Huffman 2010, 54). Admiral Saitō Makoto replaced Inukai, along with fifteen ministers, ten of whom were top military men (Goddard 2021, 149). The admiral established a militarist regime by increasingly turning to the Tōseiha faction of the Imperial Japanese Army, a group founded on their shared aggressive expansionist ideals (152). Among the various episodes of chauvinistic theatre, the May 15th Incident is the most critical origin of Japanese nationalism. The assassination marks not only the death of Inukai but also that of Taisho parliamentary democracy, reshaping the nature of governance until the end of the Second World War.

Beyond the Domestic Causes of the Assassination

As much as the May 15th Incident was the source of interwar nationalist ideology, the assassination was also a repercussion of pre-existing nationalist discontent with Western influence. As stated above, the young naval officers’ motivations were rooted in dissatisfaction with their politicians, who accepted the London Naval Treaty, a Western-dictated agreement that imposed limitations on Japan’s military capacity. In 1930, Japan yielded to Western limits to the 5:5:3 ratio of capital ships (Goddard 2021, 156). The ships were considered necessary for the execution of Japan’s international policy of maintaining peace in the Orient (Nomura 1935, 198). Nevertheless, the delegates reluctantly submitted to the ratio under the condition that Japan’s naval bases in the Far East would be conserved (Siniawer 2011, 994). However, military leaders believed that the control over their islands should have been indisputable to begin with. Bases including those in the Bonin islands, Luchu, Amami-Oshima, Formosa and the Pescadores, all “appertained” to Japan proper (Nomura 1935, 198). Meanwhile, the Treaty guaranteed the United States and Great Britain possession over their far-flung colonial possessions such as the Philippines, Guam and Hong Kong. For these reasons, public opinion considered this restriction a “disgrace,” indicating looming nationalist feelings even before Inukai’s assassination (197). Kichisaburo Nomura, an admiral in the Imperial Japanese Navy, contested this ratio’s establishment, as he stated that Japan “must be granted a position of equality with other Powers” (198). The imposition of an inferior ratio by the Western powers, which Japan considered itself equal to, was a slap in the face to the nationalists. Instead, what Japan ardently desired was the recognition of the principle of equal opportunity, which could only be achieved with their right to produce naval arms (198). Initial disappointment towards the acceptance of military restrictions developed into humiliation, as the treaty consolidated a stigma of inferiority. The London Naval Treaty’s restrictions convinced Japan that the ratio stood in the way of its mission of preserving order in the Far East. Therefore, the naval officers found it necessary to restore Japan’s prestige through the assassination of the leader who brought shame to the nation.

Japanese imperialism in an international context

The May 15th Incident transitioned domestic power from political parties to an assertive military that determined the fate of Japan’s international relations at a highly pivotal stage of the state’s modern history. In the following years, Prime Minister Saitō’s government took limited actions to keep the military in order and even less to counter the momentum of expansionist foreign policies (Maruyama and Morris 1969, 68). By the fall of 1932, the Saitō administration reversed Inukai’s efforts by extending official diplomatic recognition to Manchukuo in the Japan-Manchukuo Protocol (Saito 2017, 597). The Japanese diplomats presented Manchukuo not as a formal colony but as an independent state of “interracial harmony” for the sake of Manchurian interests (598). The expansionists in power envisioned a giant yen bloc containing Manchuria, Korea, Taiwan, and other Japanese territories. What differentiated Japanese imperial prospects from the capitalist West was that Japan’s empire would not exploit the people but “bring prosperity to all the emperor’s subjects” (599). Nationalist leaders who took office after the May 15th Incident shaped the way Japan engaged with the international world, that being imperialistic state policy. 

However, the rest of the world could not empathise with the Japanese empire’s new decision-makers and their inherent nationalism that prioritised the empire’s interests over those of the collective international community. After the Chinese delegation appealed to the League of Nations, the Lytton Commission was created with the task of investigating the causes of the Manchurian Crisis and making resolution recommendations (Times 1933). The resultant Lytton Report criticised Manchukuo as an “illegitimate puppet state” and called for the demilitarisation of the region through a multilateral conference (League of Nations 1932). Outraged, Saitō’s diplomats marched out of the Assembly and withdrew from the League (Times 1933). While the West was convinced that Japan harboured revolutionary objectives inconsistent with the international order, the Japanese found such criticism hypocritical; they considered it rooted in  the West’s colonial past. Japan rationalised its withdrawal with another round of victimisation propaganda. The press rehearsed old grievances ranging from the London Naval Treaty, the soft peace terms for Russia in 1905 and American discriminatory immigration policies, regardless of their reasonability (Buruma 2004, 69). The Japanese people believed that the West had betrayed their nation once again (70). Manchukuo was considered critical to Japan’s national security from the Chinese threat (Nomura 1935, 199). Demanding Japan’s withdrawal from her backyard was considered intolerable under any circumstances. In the words of Nomura, “The West was ganging up on Japan together with the Chinese” (Buruma 2004, 70). Despite these dramatic claims, the League failed to apply any economic or military sanctions against Japan. Great Britain and the U.S. only verbally condemned the Manchurian takeover (Maruyama and Morris 1969, 68). The ease with which militarist member-states could withdraw from the League’s commitments indicated that the governmental body meant to protect the international order lost credibility. Through expansionist claims into China, Japanese nationalist leaders promoted their imperial ambitions at the cost of preserving international peace.

No matter how hard the Japanese would claim otherwise, Manchukuo was simply a paradigm of imperial conquest. Only a government in pursuit of its self-interest would pay a tremendous price for the “great imperialism experiment” of Manchukuo (Matsusaka 2001, 3). Anderson argues that the Japanese desire to replicate the imperial conquests of European dynasties prompted Imperial Japan’s “official nationalist” policies that ravaged Asia (Anderson 2016, 94). In the pursuit of arousing nationalist sentiment, imperialists adopt this top-down approach of “defining themselves in national terms” while extending their authority beyond their borders (94). Indeed, the Japanese Empire was on a mission to establish its Emperor as a figure akin to European monarchs. Japan aspired for its Emperor to act as “the preserver of peace in the Orient” (Matsusaka 2001, 6). Manchurians were subject to policies “for which the European model was an established working practice” (96). Anderson parallels the people of British colonies with “Japanified” Manchus who were forced into the Japanese education system but never granted access to the metropole. Moreover, the scholar notes the inevitable contradiction of official nationalism when the imperial power forces the oppressed subjects to agree with their agenda to be considered nationalists (2016, 104). In interwar Japan, popular nationalism initially overthrew the democratic government because it did not work for the populace’s interests. Yet the very same nationalist groups implemented official nationalist policies in Japan’s colonies to create an Eastern bloc. Accordingly, the international system at that time was deeply influenced by the Japanese Empire’s domestic violence and imperialist foreign policies. 

Oddly enough, even Saitō was assassinated by another group of young army officers during a military revolt in 1936 (Buruma 2004, 80). However, at this point of the interwar period, the military was so powerful and the general population so condoning of their aggression that no one leader could be held responsible for Japanese imperialism. In the same year, the Kwantung Army, the largest group of the Japanese Imperial Army, incited the Marco Polo Bridge Incident to invade further into China with cabinet support (83). The escalating militaristic logic of the government drove Japan towards expansionism while moving further away from its Western allies (90). Following the May 15th incident, Japan positioned itself in a new relationship with the international order, becoming characterized by its disobedience to internationally upheld values of state sovereignty and cooperation.

Conclusions

The assassination of Prime Minister Inukai served as both a catalyst and consequence for the Japanese development of nationalist sentiments, aligning with Anderson’s idea of popular nationalism. The causes stemmed from deep-seated resentment towards Japan’s established international relations at the time, in which its empire was perceived as inferior to the West. The effects consisted of social acceptance of political violence and the opening of positions of power that hard-line militarists then filled. In the broader international context, the May 15th Incident influenced Japanese foreign policy in the form of expansionism in the Far East. Angered by the West’s condemnation, nationalist sentiment was re-established in the Japanese colonies in the form of official nationalism. Anderson’s theory on the contradictions of popular and official nationalism is highly relevant to Japanese nationalist sentiment in the 1930s. In applying his perspective, it becomes evident how the nationalist sentiment among the general population overthrows authority figures that fail to serve their country’s best interest, while simultaneously provoking violations of foreign countries’ sovereignty. Although Japanese nationalists denounced the expansionist policies of Western powers, Japanese imperialism was merely a replica of the West’s. The nationalist sentiment that led to the unjust assassination of a Prime Minister’s murder marked the starting point of Japan’s years-long injustices perpetrated against the Far East.

References 

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