Japan and South Korea must master transactional diplomacy

Southwest of Tokyo lies the quaint city of Nara. As the capital of Imperial Japan from AD 710 to 784, Nara gained renown for its historic shrines and roaming deer, the latter of which crave being fed Japanese snacks (senbei) by visitors. Nara Prefecture is also the hometown of Japan’s prime minister, Sanae Takaichi.

Self-styled as Japan’s answer to Margaret Thatcher, Takaichi’s premiership has been characterised by one of the most robust increases in defence spending and shifts in security policy since the Second World War, not least the relaxation of decades-old rules governing arms exports. Both Japan and South Korea have realised that their regional and global security environments are worsening. This is not only a result of isolated threats from an ever more aggressive Beijing or a nuclear Pyongyang. Rather, alliances old and new, including growing ties between Russia and North Korea, have been accompanied by heightened collusion between Moscow, Beijing, Pyongyang and Tehran. For Seoul, Tokyo and Washington, the individual and collective threats posed by these alignments of authoritarian actors can no longer be ignored.

The junior partner in any alliance fears two possibilities: the first is entrapment, wherein they can do little but follow their senior partner’s edicts, whether that means being dragged into an unwanted war or otherwise. The second is abandonment, a fear that is increasingly on the minds of policymakers in Tokyo and Seoul. President Trump’s announcement of the scaling-down of the annual US-South Korean Ulchi Freedom Shield military exercises on 16 August, hours before the drills were due to begin, caused unease in Seoul. Whether on grounds of cost, a penchant to revive talks with Kim Jong Un or a combination of the two, this was not the first time Trump had performed such an act. During his first administration, similar drills were downsized and cancelled.

Fears of such abandonment are not new. After the Korean War Armistice Agreement was signed in July 1953, and as South Korea’s army expanded, President Eisenhower called for a drawdown of US forces on the Korean Peninsula. Troop numbers dropped from over 325,000 in 1953 to little more than 75,000 in 1955. Nearly two decades later, the Nixon administration’s Guam Doctrine led to a further reduction in troops to a little over 40,000 by 1971, a retrenchment that catalysed South Korea’s own – albeit abortive – ambitions for nuclear weapons. More recently, under George W. Bush, approximately 3,600 troops were redeployed to Iraq in 2004, never to return to the peninsula.

Yet, the West’s allies must realise that the world of today is nothing like that after the Second World War, in which Washington financed the rebuilding of what was to become East Asia’s security architecture. The signing of mutual defence treaties, notably with Seoul and Tokyo, and the bolstering of alliances have become invaluable in deterring an expanding array of threats. Today’s world, however, shows that not all alliances are the same. Russian Foreign Minister Sergey Lavrov claimed recently that the ‘invincible alliance’ between North Korea and Russia is fighting to establish a ‘new’ and ‘just’ world order.

Even though Moscow, Pyongyang, Beijing and Tehran use similar rhetoric to that of the US and its allies to describe their relations (such as ‘comprehensive’ and ‘strategic’), what makes these new sets of authoritarian alliances particularly concerning is that not all of them are codified. The members of this deadly quartet have neither signed any treaty nor pledged adherence to a common framework. The specifics of any respective bilateral alliance are also shrouded in secrecy.

Facing these new alignments in global politics, Washington’s longstanding ironclad alliances with Seoul and Tokyo need to be strengthened, but Seoul and Tokyo cannot simply expect their larger ally to do all the work. For all the supposed shared values between Washington’s allies and partners, like-mindedness does not preclude competition for the attention of a common senior ally. Discussions surrounding the redeployment of Patriot missile batteries from South Korea to the Middle East, in March and April this year, underscore this reality.

South Korea’s progressive president Lee Jae Myung has spent his first year in power trying to move away from his pre-election jibes against the US-South Korean alliance. One of his first manoeuvres after having met President Trump in August 2025 was to raise defence spending for 2027 to an all-time high of 73 trillion South Korean won (just over $54 billion), a significant increase of 8.2 per cent from the previous year. This justified move, coupled with Seoul’s commitment to raise defence spending to 3.5 per cent of its GDP by 2035 (current levels amount to approximately 2.3 per cent), is indicative of a realisation that, amid a deteriorating regional and global security environment, Seoul must simultaneously strengthen its relationship with Washington while taking steps to modernise this alliance.

Rhetoric, however, is not synonymous with reality. For Seoul, bolstering its alliance with Washington means following through promptly on prior commitments. Despite having pledged almost a year ago to invest $350 billion in the United States (in response to a reduction in US tariffs on South Korean exports, from 25 to 15 per cent), South Korea’s dithering has understandably irritated the White House. Faced with the threat of possible tariff hikes, following a recent visit to Washington, South Korea’s Trade Minister, Kim Jung-kwan, stressed how negotiations for a $100 billion investment into nuclear power plants and natural-gas projects are now in their final stages.

In contrast, in July 2025, Japan legally committed to investing $550 billion into the US economy until 2029 and has so far launched two energy and manufacturing infrastructure projects totalling $109 million. Japan’s promptness, agreeing to transfer funds within 45 days of the US selecting a particular investment project, reflects a recognition within Tokyo that boosting defence spending and reinforcing the alliance with the United States go hand in hand: the former reinforces the latter.

Yet this difference between Seoul and Tokyo must also be understood with respect to the perennial question of domestic politics. In contrast to his Japanese counterpart, South Korea’s Lee Jae Myung faces constraints from his own party and voter base, for whom strengthening ties with Washington remains contentious.

When I visited Nara earlier this month, the deer were far from shy or deferential. The sight of me holding a pack of senbei drove a small herd to fight over every morsel. The stag scoffed most of them, leaving the rest to fend over the dregs. Like the senbei, the United States is a scarce resource. Washington must commit itself to its East Asian allies: the security of the Korean peninsula is a direct security interest of the United States. Nevertheless, as the West faces an expanding number of threats, Washington’s attention cannot stretch into infinity. Just as the stag did not wait to push past the rest of the herd, Seoul and Tokyo must recognise that allies who hesitate at a moment of opportunity risk being outpaced by a quicker partner. While there is as yet no active US retrenchment from East Asia, ironclad does not mean unconditional. As in any herd, the deer that dithers goes hungry.