Relations between South Korea and Japan have been historically complicated, especially when it comes to military defence. The fallout of decades of Japanese colonial rule over the Korean Peninsula left the subsequently formed state deeply suspicious of any and all Japanese military activity, lest it betray a renewed militaristic outlook. Nevertheless, the recent announcement of an unprecedented increase in military spending (from 1% to 2% of Japan’s GDP) that came with the newly unveiled National Defence Plan not only elicited the habitually strong response from South Korea, it was partly encouraged. While this implies a possible change in dynamics when it comes to Japan’s role in the collective defence of East Asia, it would be unwise to assume that historical outlooks and disputes between the two countries have been even partially abandoned. Rather, Japanese actions and South Korean response to them need to be understood in the wider geopolitical context in the region, and the persistent challenges, both old and new, that face the Trilateral US-Japan-ROK defensive alliance.

Japan’s expansion of military defence capabilities comes as a response to the usual, but recently quite pronounced security threats coming from North Korea (mostly in the nuclear domain) and China (mostly in the conventional and naval domains) as perceived by the Trilateral alliance. As a response, South Korea has signalled openness to greater defence cooperation in the region along with the United States. However, Japan’s new policy has not remained without criticism. The South Korean Foreign Ministry demands that the country be consulted in case of any use of Japan’s new capabilities on the Korean Peninsula. Additionally, its warnings for Japan not to forget the lessons of its past are a stark example that South Korea is not ready to let bygones be bygones. Among the most frequently voiced arguments, however, is that the new National Defence Plan goes against Japan’s long-standing pacifist policy, one that has been firmly enshrined in the country’s constitution since its military defeat in 1945. This is a claim advanced among others by China as well as Russia, which both criticised the expansion. Japan argues otherwise in a new reinterpretation of that constitution. While an increase of spending to 2% still lags behind that of the third nation in the alliance, the United States (3.1% in 2022), as South Korean officials rightly point out, this is incommensurate with South Korea’s own capabilities, since the country’s economy only amounts to a third of that of Japan. For the moment, it appears as though South Korea and Japan thus continue to walk the tightrope of slow reconciliation.

This issue of war memories and reconciliation has plagued Japan-ROK relations since the end of WWII, and issues of history have consistently been used by political actors in both countries for domestic and international policy reasons. Without an understanding of the history of the region, and Japan’s pivotal role in it, it is impossible to fully comprehend the complex political and relationship, with all its ups and downs, that exists between the two nations. As a former colonial empire, Japan at its peak held control over most of East Asia, including the entirety of the Korean Peninsula, Taiwan, and most of northeastern and eastern China. As a result, many of the eventual new states in the region and their identities were forged in a period of war and struggle for independence, as is the case with the Korean nation, present-day South Korea included. In South Korea, issues with the ‘correct view’ of history and its insistence on Japanese recognition of this view continued to sour its relations with the latter. As it pertains to Japanese military defence policy, expansion in the area provokes the ready response of suspicion and accusations of a return to the militaristic ideology of the past. For this reason, the relatively mild response of South Korea to the present changes in Japanese defence policy betray not only a more considerate domestic outlook in both countries (further evidenced by Japanese insistence that new capabilities will serve primarily for defensive rather than offensive purposes), but a greater perception of threat by South Korea in the region presently.

Map of the Japanese empire (1870-1942)

With the current governments of Japan and South Korea, under the Kishida and Yoon administrations respectively, it is unlikely that tensions to do with historical issues would impede defence cooperation in the region. With both administrations coming from the more dovish factions of their respective political parties, bilateral views and relations are likely to remain lukewarm if cautious. Nevertheless, with the new Japanese National Defence Plan encompassing a period of five years, during which administrations will inevitably change, the positive outlook of regional cooperation might not continue beyond this point. Future interpretations of Japanese military defence expansion are most probably going to be dependent on a range of domestic as well as broader strategic security factors. Only time will tell whether disputes over history or the persistence of geopolitical risk will prevail in South Korean foreign policy decision-making.