China Joins SEANWFZ: What Gains and Anxieties Await ASEAN?

Thiên Ngân wrote this article in Vietnamese and published it in Luat Khoa Magazine on July 14, 2025. 

In a noteworthy move, Malaysian Foreign Minister Mohamad Hasan announced on July 10, 2025 that China is ready to sign the Treaty on the Southeast Asia Nuclear Weapon-Free Zone (SEANWFZ) “without any conditions attached.” [1] If this materializes, China would become the first nuclear-armed state to do so, a highly symbolic gesture laden with strategic calculations that reinforces Beijing’s international standing. [2]

While China’s readiness to sign bolsters ASEAN’s regional stature, it also presents a new set of risks that the bloc must carefully scrutinize. The decision has significant implications for both ASEAN and the broader regional security architecture, raising questions about China's objectives and the potential consequences of its participation.

SEANWFZ: A Security Shield for Southeast Asia

Signed on December 15, 1995, the SEANWFZ Treaty—also known as the Bangkok Treaty—represents a collective effort by ASEAN nations to establish a Southeast Asia completely free of nuclear weapons by preventing their development, production, possession, testing, deployment, and transport. [4] The initiative was designed to address the security risks posed by the superpower arms races of the Cold War, and its relevance endures today amid lingering tensions between the United States, China, and Russia.

Strategically, the treaty holds powerful symbolic weight, projecting ASEAN’s resolve to distance itself from global power competition and reinforcing the bloc’s image as a mediator in maintaining international order. 

This commitment was recently reaffirmed at the 58th ASEAN Foreign Ministers' Meeting, where Malaysian Foreign Minister Mohamad Hasan declared, “In the face of the continuing threat that nuclear weapons pose to humanity, I urge all ASEAN member states to stand united in our efforts.” [3]

What sets SEANWFZ apart is its invitation to the five recognized nuclear-weapon states (the P5)—the United States, Russia, China, France, and the United Kingdom—to sign a protocol pledging not to use or threaten to use nuclear weapons within the region. [5] To date, however, only China has expressed serious and unconditional goodwill toward signing.

China’s Eagerness to Join SEANWFZ

For nearly three decades, Beijing avoided signing the SEANWFZ Protocol, concerned that it might constrain its military freedom of action in the South China Sea. So why is China now suddenly willing to sign unconditionally? The move appears to be a calculated diplomatic maneuver driven by three key strategic interests.

First, it is a soft power play aimed at reinforcing China's image as a “responsible major power” at a time when it faces mounting criticism for its coercive behavior in the South China Sea and Taiwan Strait. Signing the treaty allows China to score diplomatic points with ASEAN and counter the expanding U.S. military footprint in the region, particularly the AUKUS security pact. As Chinese Foreign Ministry spokesperson Mao Ning stated, “We have repeatedly expressed China’s readiness to take the lead in signing the Protocol to the SEANWFZ Treaty.” [6]

Second, joining SEANWFZ allows Beijing to de-escalate diplomatic tensions with ASEAN claimants like the Philippines and Việt Nam. It offers a chance to redirect regional dialogue away from hard security issues and its own aggressive actions toward more cooperative topics like nuclear disarmament—thus blunting regional criticism over its aggressive behavior in the South China Sea.

Finally, China likely sees the treaty as a tool to exert indirect pressure on the United States within their broader geopolitical rivalry. As the Trump administration pressures Southeast Asian nations with coercive tariffs, Beijing can position itself as a more amicable and responsible “guardian of peace,” thereby enhancing its regional influence.

Is This a “Victory” for ASEAN?

China’s decision to sign the SEANWFZ Treaty could be seen as a clear diplomatic win for ASEAN. The mere fact that Beijing recognizes the value of a region-led initiative under ASEAN’s leadership is notable. Compared to the long-stalled Code of Conduct (COC) for the South China Sea, persuading China to sign the treaty can be seen as proof that the bloc still retains the ability to “set the rules of the game.” [7] Furthermore, China’s accession would bolster the treaty’s legal weight, adding a layer of protection for Southeast Asia against nuclear threats.

However, this apparent victory carries unpredictable and significant risks. The price for China’s participation could be high. Once it signs, Beijing might demand that ASEAN accept its own interpretation of the treaty’s territorial scope—for example, by excluding disputed areas in the South China Sea. This would not only set a dangerous precedent but also undermine the neutrality ASEAN has worked to uphold.

Another potential risk is that China’s signature could be used as a diplomatic tool to dampen concerns among some ASEAN members about Beijing’s coercive behavior in the region—such as its actions against the Philippines in the South China Sea. This could weaken the bloc’s internal momentum and resolve to form a unified response to China’s assertiveness.

What Future Lies Ahead for the Regional Security Architecture?

If China follows through on its promise to sign the SEANWFZ, it would mark a significant milestone and could provide momentum for deeper discussions on an ASEAN-centered regional security architecture. However, Beijing could skillfully use this commitment to secure strategic advantages without making any substantive concessions. If China signs the treaty but continues its assertive actions in the South China Sea, the agreement risks becoming a symbolic document with little enforceable weight.

Rather than rushing to celebrate, ASEAN must seize this opportunity to define a clear and transparent implementation framework for the treaty, complete with an independent monitoring mechanism. This is a crucial moment for the bloc to demonstrate its resolve by upholding a neutral stance and proving that its initiatives are not only meaningful in principle but also effective in practice.

Ultimately, China’s declaration is a notable signal, but behind this apparent goodwill lie long-term strategic calculations. ASEAN must proceed with caution to safeguard its collective interests through clear and enforceable commitments, avoiding the trap of accepting “words unbacked by actions”—a pattern Beijing has employed on multiple occasions.