As the new year unfolds, China finds itself grappling with strategic pressures fuelled by two US treaty allies at its doorstep – Japan and South Korea. In the second of a two-part series, Seong Hyeon Choi looks at how competing pressures in the Korean peninsula may complicate China’s security calculus.
In 2025, there was a major shift in China’s security environment relating to the Korean peninsula, as the North grew more open in its push for nuclear weapons and the South leaned closer to the United States.
South Korean President Lee Jae Myung, who took office last June, has sought to follow treaty ally Washington’s new national security strategy, which urges Indo-Pacific allies to increase their input into collective defence within the first island chain.
It has led to South Korea ramping up its advanced capabilities, including gaining US President Donald Trump’s approval to build nuclear-powered submarines and attempting to “modernise” the alliance with the US, which would see more investment flowing into the country for conventional defences against the North.
Meanwhile, ties between Beijing and Pyongyang have thawed, highlighted by North Korean leader Kim Jong-un’s first visit to China in six years for the military parade in Tiananmen Square in September.
Relations had been strained by Pyongyang’s nuclear and missile tests, which Beijing viewed as destabilising, as well as Kim’s growing military ties with Russia, challenging traditional Chinese influence.
But Pyongyang has grown more open about its progress in developing nuclear weapons, while Beijing has rolled back its stance opposing nuclear weapons on the peninsula.
Observers expect China to seek stronger ties with North Korea this year, despite its increasing nuclear capabilities. This coincides with Chinese attempts to respond to US rivalry in the Indo-Pacific region and South Korea’s increased military capabilities, which could pressure Beijing’s northeastern strategic flank.
On Sunday, Lee arrived in Beijing for a four-day state visit to China, the first South Korean president to visit since 2019. At a summit with Xi on Monday, the two leaders agreed on the need to resume dialogue with North Korea and restore bilateral relations through resuming cultural exchanges, according to the South Korean presidential office.
According to Lee, who was speaking to reporters in Shanghai, during the summit Xi said “patience” was required to resolve the North Korean nuclear weapons issue, in response to Seoul’s request for Beijing to mediate between the two Koreas.
Even as it tries to restore ties with Beijing, the Lee administration has faced pressure from Washington to invest more in collective defence against Chinese advances across the first island chain.
In October, following Trump’s meeting with Lee on the sidelines of the Asia-Pacific Economic Cooperation (Apec) summit in South Korea, the US president announced on social media his approval for Seoul to build nuclear-powered submarines.
Lee had asked Trump to “allow fuel supply for nuclear-powered submarines”, and for negotiations to proceed on uranium enrichment and the reprocessing of spent nuclear fuel. He said the diesel-electric submarines Seoul operated had limited submersibility, limiting their tracking activities against North Korean or Chinese subs.
Nuclear-powered submarines are powered by nuclear reactors but are not necessarily armed with nuclear weapons. Compared with conventional diesel-electric submarines, which require frequent resurfacing for refuelling, nuclear reactors allow the submarine to operate underwater at a higher speed for an extended period of time, essentially with unlimited range.
Because of their advantages in stealth, speed and endurance, nuclear submarines have played a crucial role projecting maritime deterrence in blue waters. But the use of nuclear reactors – which require technology for uranium enrichment, also used to build nuclear weapons – has limited the possession of nuclear-powered submarines to the major nuclear powers: the US, Russia, China, Britain, France and India.
While the construction of the boats would require at least a decade, the South Korean Navy’s operation of nuclear-powered submarines would be likely to prompt a greater push from the US for them to be used for collective defence in the Indo-Pacific region. The South Korean government has said it would not target any specific country.
Jonathan Fritz, principal deputy assistant secretary of state for East Asian and Pacific affairs at the US State Department, last month described Trump’s support for South Korea building nuclear-powered submarines as a “clear example” of bilateral cooperation that advanced their “collective capabilities against regional threats”.
In November, Admiral Daryl Caudle, US chief of naval operations, said that once South Korea fielded a nuclear-powered attack submarine, the US would have a “natural expectation” for it to play a role in its broader plan to counter China, which he described as a “pacing threat”.
Stephen Nagy, a professor of politics and international studies at the International Christian University in Tokyo, said Beijing viewed Seoul’s nuclear submarine programme as “destabilising” the regional balance and “potentially emboldening South Korean strategic autonomy”.
“While a single South Korean nuclear submarine won’t fundamentally challenge China’s quantitative naval superiority, it represents a qualitative leap in allied undersea persistence in critical chokepoints, forcing China to divert more resources to anti-submarine warfare,” Nagy said.
It appears likely that South Korea will share the burden for collective defence in the first island chain with the US as the two countries also move to “modernise” the alliance under the Trump and Lee administrations. It would allow strategic flexibility for US Forces Korea (USFK) operating in the region while South Korea leads the defence against North Korean threats through the transfer of wartime operational command from the US to South Korea.
Last month, while outlining the national defence strategy, US Defence Secretary Pete Hegseth referred to South Korea as Washington’s “model ally” for stepping up for its own defence. He said Seoul had committed to spend 3.5 per cent of its GDP on core military spending and assume the leading role in its conventional defence.
Commenting on the regional implications, Liselotte Odgaard, a senior fellow at the Hudson Institute in Washington, said Seoul’s operation of a nuclear-powered submarine (SSN) in the region and beyond would complicate Beijing’s military activities.
“South Korea is transitioning from a regional defence contributor to a strategic ally capable of supporting broader deterrence. In operational terms, South Korean SSNs will complicate China’s naval activity by threatening [People’s Liberation Army] movements and bolstering allied undersea deterrence,” Odgaard said.
“Diplomatically, however, China can still mobilise pressure, though a full confrontation seems unlikely unless South Korea aggressively deploys beyond traditional defence boundaries focused on North Korea.”
China has so far shown only a lukewarm response to Seoul’s plans to build nuclear-powered submarines, simply urging South Korea and the US to abide strictly by non-proliferation commitments and act in the interest of regional peace.
Odgaard said China’s restrained tone suggested recognition of broader geopolitical relations and a desire to avoid a flashpoint, such as that sparked by the THAAD issue in 2016, when South Korea deployed the US Terminal High Altitude Area Defence anti-missile system, triggering Beijing’s ire.
“Although at present China is responding in moderate terms, China is wary of a potential arms race,” she said. “If South Korea’s submarines are seen to add to US maritime operations against Chinese interests in the region, China may eventually increase pressure on South Korea.”
Nevertheless, China has also toned down its stance on North Korea’s nuclear programme, despite decades of opposition to Pyongyang’s possession of a nuclear arsenal.
In 2021, Kim declared that North Korea planned to build its own nuclear-powered submarine.
Doubts about Pyongyang’s technical feasibility were dispelled in March last year, when Kim visited the shipyard that was reportedly building a “nuclear-powered strategic guided-missile submarine”.
Kim again inspected the new nuclear-powered submarine in December. According to the North’s state-owned Korea Central News Agency (KCNA), the boat will have a displacement of 8,700 tonnes, marking “a leap forward in bolstering the combat capabilities of our fleets”.
Kim warned that South Korea’s nuclear-powered submarine plans would “worsen the instability” on the Korean peninsula, according to KCNA.
The development was an “offensive act” that risked “severely violating” the North’s security and maritime sovereignty, Kim said, vowing that any threat to its security would trigger a “merciless retaliatory attack” through the “responsible exercise of its “true nuclear war deterrent”.
North Korea’s new submarine forms part of recent efforts to advance its nuclear programme and conventional weapons capabilities, a drive that has especially picked up steam since Russia invaded Ukraine in 2022. Pyongyang has supplied Moscow with troops and weapons in the armed conflict in exchange for Russian aid and weapons technology.
China’s November white paper on arms control, disarmament and non-proliferation did not mention its long-standing support for denuclearisation of the Korean peninsula, calling only for “peace and stability” there.
The omission diverged from the previous 2005 white paper, which explicitly said “China supports denuclearisation of the Korean peninsula” – wording that critics read as tacit acceptance of North Korea’s possession of nuclear arms.
The latest white paper comes against the backdrop of improving China-North Korea ties. Kim’s attendance at the September 3 military parade in Beijing marked not only his first visit to China in six years but also his first multilateral diplomatic event – where he held summits with Chinese President Xi Jinping and Russian President Vladimir Putin.
During their talks after the parade, Xi and Kim pledged to “strengthen strategic coordination in international and regional affairs to safeguard common interests”, according to Chinese state media.
The summit also did not mention the denuclearisation of the Korean peninsula, in contrast to the one in 2019, when Xi last visited Pyongyang. Xi told Kim at the time that China was willing to play a “positive and constructive role in achieving denuclearisation of the Korean peninsula and long-term stability in the region”.
Another sign of China’s more open acceptance of Pyongyang’s nuclear weapon development came in October, when Li Qiang became the first Chinese premier to visit North Korea, as Pyongyang rolled out its latest solid-fuelled Hwasong-20 intercontinental-range ballistic missiles (ICBMs), reportedly built with technological help from Russia.
Although it has not yet tested the missile, North Korea tested a new solid-fuel rocket engine in September, which state media said would be used for future ICBMs. KCNA has described the new missile as “the most powerful nuclear strategic weapon system”.
The use of solid fuel is likely to reduce the time needed to prepare the missile for launch, and it reportedly uses carbon fibre composites – which could help reduce the missile’s weight and make it harder to detect.
North Korea’s nuclear developments is also seen by some as signalling pressure on China-South Korea ties.
On Sunday, Pyongyang conducted a hypersonic missile launch drill, overseen by Kim. He said it was a “very important strategic task” to maintain and expand a “powerful and reliable nuclear deterrent” for North Korea’s national defence, according to KCNA.
The drill took place on the same day Lee departed for his state visit to China and a summit with Xi, suggesting a potential dilemma for Beijing in balancing its ties with Seoul and Pyongyang.
According to Lim Eul-chul, a professor at Kyungnam University’s Institute for Far Eastern Studies, Pyongyang is trying to prevent closer ties between South Korea and China.
“It is also a containment message to China regarding the possible discussion over the denuclearisation during the summit,” he said.
However, Lim noted that China now “understands North Korea’s position much better than before,” and even viewed Pyongyang as a more crucial strategic asset.
“Previously, the North Korean nuclear issue was perceived as a significant threat to peace and stability on the Korean peninsula,” said Lim. “Now, North Korea’s nuclear development, while they may not officially state it, could actually function as a deterrent.”
Nagy said Beijing would deepen ties with Pyongyang despite the ICBM developments because North Korea served as an “indispensable buffer and bargaining chip”, particularly as the US-China competition intensified.
“Beijing calculates that the benefits of keeping Washington and its allies preoccupied with North Korean provocations far outweigh the risks of Pyongyang’s growing nuclear capabilities, which aren’t aimed at China anyway,” Nagy said.
North Korea has advanced its nuclear programme even as Lee and Trump have sought to revive denuclearisation negotiations with Kim.
While Kim has remarked about “good memories” of his talks with Trump during the US president’s first term from 2017 to 2021, he insists that the US must “discard its delusional obsession with denuclearisation”. Kim has also pushed for US recognition of North Korea as a nuclear state while ruling out any talks with South Korea.
Meeting Xi on the margins of the Apec summit on November 1, Lee urged him to help restart talks with Pyongyang.
Odgaard said China could be “expected to maintain, and even strengthen” its ties with North Korea, as it valued the country as a buffer against US-aligned South Korea and the USFK – which was of greater concern for Beijing than missile proliferation.
“South Korean calls for Chinese mediation highlight Beijing’s central role in preserving stability on the Korean peninsula. The asymmetric partnership, stemming from the Korean war, is underpinned by China’s desire to prevent a sudden regime collapse, which it views as a greater threat than Kim’s missile programme,” she said.
“The ideological link between China and North Korea also remains strong ... reinforcing cooperation as China’s own geopolitical rivalry with the US intensifies. China views North Korea as part of a tactical alignment among powers that oppose the US, such as Russia, and they can help offset US influence.”
Odgaard added that Kim’s recent summit with Xi signalled a “thaw” in China-North Korea relations and closer strategic alignment.
“Nevertheless, China is likely to deepen security and economic engagement with North Korea without fully endorsing ICBM advancements, signalling that regime survival and strategic depth remain the main Chinese priorities,” she said. -- SOUTH CHINA MORNING POST
