This move comes at a time when the South Korea–US alliance is experiencing a level of strain unseen for nearly 20 years. The strain is coming from the White House’s exorbitant financial demands for the maintenance of United States Forces Korea as well as US pressure on South Korea not to withdraw from the GSOMIA intelligence-sharing pact with Japan.

The official purpose of the South Korea–US defence partnership has for decades been to deter a conventional attack on South Korea from North Korea, while pragmatically also preventing South Korea from undertaking the forceful unification of the Korean Peninsula under Seoul’s authority.

Yet in recent times the rise of China has given a new sense of purpose to the South Korea–US alliance. Recent polls from both the Chicago Council on Global Affairs and the Seoul-based Asan Institute indicate that support for the alliance remains strong — in part because the publics of both South Korea and the United States view it as a tool to counter China.

Proposals have also emerged aimed at modifying the alliance to have South Korea participate in contingencies involving the United States outside the Korean Peninsula, such as in the South China Sea. There is an interest in expanding the scope of the alliance from South Korea’s historically limited and ad hoc support of American military undertakings in other regions of the world to a more permanent role.

But South Korea will face the brunt of any deliberate repurposing of the alliance to position the United States against China. A rough parallel to this can be seen in the evolution of NATO’s purpose after the Cold War.

US policymakers in the 1990s believed that NATO expansion was best for European security, even as it went against promises Washington had previously made to Moscow. Russia’s aggressive actions against Georgia and Ukraine — and a looming threat in other neighbouring states — have been a direct response to an otherwise unprovoked geopolitical encirclement of Russia by the West.

The question policymakers in Seoul need to be asking is whether or not the maintenance of the current security arrangement with the United States is worth the risk of being entangled in Washington’s profound scepticism toward China’s rise. Likewise, Washington must consider the possibility of alienating South Korea by asking Seoul to extend the mandate of their alliance to a wider scope of balancing against China.

Conventional wisdom predicts that South Korea will eventually have to choose outright political alignment with either China or the United States. Still, South Korea is showing a propensity for taking its own stance when it comes to relations with China outside the framework of great power tensions.

Following the breakdown of China–South Korea relations in 2015–2016 due to the controversy over the US deployment of the Terminal High Altitude Area Defense (THAAD) missile defence system, South Korean President Moon Jae-in embarked on a ‘reset’ of relations with Beijing. This reset helped smooth the way for the 2019 China–South Korea strategic dialogue — the first such discussion between China and South Korea since 2014.

A military hotline between Beijing and Seoul that was opened in 2015 was also put to good use in October 2019 when the Chinese air force notified South Korea that its aircraft were approaching South Korea’s Air Defense Identification Zone.

While China’s retaliatory economic measures against South Korea in 2017 did not reverse Seoul’s decision to deploy THAAD, they did show that the United States will not necessarily come to the aid of an ally bearing the brunt of economic warfare. It seems this was the reason behind South Korea’s decision to issue the so-called ‘three noes’ to China regarding Seoul’s alignment with the United States — no additional THAAD deployment, no participation in US missile defence and no US-Japan-ROK trilateral military alliance.

Likewise, despite a shared threat from North Korea to Seoul, Tokyo and Washington, South Korea has placed what it considers to be its own national interest ahead of security multilateralism. South Korea’s decision to withdraw from the GSOMIA intelligence-sharing pact highlights that South Korea is willing to break with another US ally in Northeast Asia. It also shows there is no guarantee South Korea can be expected to toe the US line when it comes to China.

The decades-long South Korea–US alliance, buttressed as it is by an unprecedented level of interconnectedness between two national militaries, is unlikely to end any time soon. But as long as the alliance remains, it ought to stay within its original purpose of ensuring South Korea’s security against the threat of attack from North Korea. Overextending the alliance’s mandate will only place more tensions on a partnership already under stress.

Anthony V Rinna is Senior Editor and specialist on Russian foreign policy in East Asia for the Sino-NK research group.