- The South China Sea to the Taiwan Strait: Asia’s Security Order in Flux
The ocean lanes of the Indo-Pacific are increasingly tense: from the contested features of the South China Sea, across the narrowing waters of the Taiwan Strait, to the island-chains wrapping around Japan’s southwestern flank, a new architecture of danger and opportunity is emerging. The security order that Southeast Asian nations long assumed to be reasonably stable is now in motion — and a central actor in this change is Japan.
Japan’s security identity is undergoing what many analysts regard as its most dramatic transformation since 1945. In December 2022, Tokyo released a new trilogy of strategic documents — the National Security Strategy of Japan (NSS), the National Defense Strategy of Japan (NDS) and the Defense Buildup Program (DBP) — that together signal a decisive re-calibration of Japan’s defence posture.
One of the clearest indicators: Japan has set the ambition to raise its defence spending to 2 per cent of GDP by 2027.
Japan’s fiscal year 2025 defence budget request of ¥8.73 trillion (roughly US $55 billion) demonstrates that this isn’t mere signalling.
Also striking: Tokyo has committed publicly to acquiring “counter-strike” or “strike-back” capabilities — long-range systems capable of hitting adversary targets earlier and farther from Japanese territory.
These shifts have immediate ripple effects in Southeast Asia. They are altering the calculus of maritime states — especially the Philippines and Vietnam — who see new openings but also face strategic dilemmas. Japan is evolving, in the eyes of many in the region, from a peripheral security actor to a major player — one whose trajectory Southeast Asians cannot afford to ignore.
For decades Japan’s defence posture was shaped by the legacy of its 1947-postwar constitution and the so-called pacifist consensus: minimal military ambitions, substantial reliance on the United States Armed Forces alliance, and a broader strategy of economic diplomacy. But the security environment around Japan has changed dramatically: the increasingly assertive posture of China, the missile and nuclear threats from North Korea, and the war in Ukraine have all sharpened Tokyo’s risk perception.
The NSS 2022 states that Japan will “make the defence of Japan’s territory and people its first priority” and that possessing capabilities to “disrupt and defeat invasions against Japan much earlier and at a further distance” is necessary.
significantly upping its defence budget and procurement of advanced systems.
loosening prior restraints on arms exports and allied access to Japanese territory.
expanding the role of non-traditional security domains (cyber, space, intelligence) alongside maritime and missile defence.
deepening its cooperation not only with the U.S. but with other “like-minded” partners in the Indo-Pacific.
In short: Japan is moving from a defence posture oriented almost exclusively toward self-defence under U.S. protection, to one that projects deterrence, aids regional resilience, and treats maritime-domain security as a primary mission. This is not a full revolution of Japanese strategic culture (many core principles remain) but it is an acceleration of Japan’s trajectory at a “giant-leap” pace.
For the member states of the Association of Southeast Asian Nations (ASEAN), Japan’s turn presents both tangible opportunities and strategic headaches.
Tokyo’s new ambition is providing capacity-building options for Southeast Asia’s maritime states:
Japan has established a new “official security assistance” (OSA) scheme — distinct from its traditional Official Development Assistance (ODA) — to supply partner states with radars, boats, surveillance equipment and the like.
The Philippines, for example, has received coastal radars and signed a Reciprocal Access Agreement (RAA) with Japan, enabling joint logistics and exercises. (While I did not locate a direct citation at this moment for the RAA with Manila, the framework is widely referenced.)
Vietnam secured a ¥36.6 billion loan via the Japan International Cooperation Agency (JICA) to build coast-guard vessels — a direct signal of Tokyo’s maritime capacity-building thrust.
These kinds of moves matter: for smaller maritime states wary of Chinese incursions, enhanced domain awareness, improved sea-guard assets, and better logistics are tangible game-changers. And because Tokyo is not positioning these as alliance commitments (at least not formally) they are more palatable to hedging states that want capability but not overt bloc alignment.
The maddening reality of hedging in 2025 is that neutrality is harder to maintain. States deepening cooperation with Japan may face Beijing’s ire — economically, diplomatically, or through coercion. Japan’s growing profile inevitably raises Chinese perceptions of containment or coalition-building.
Countries like Indonesia or Malaysia, which have substantial economic ties with China while also managing maritime stakes, may find themselves squeezed by Tokyo’s shift. Staying ‘non-aligned’ becomes increasingly expensive and politically awkward.
There is a risk of over-reliance on Japanese industrial capacity. Tokyo’s defence-industrial exports are opening up (for example, Japan now permits the export of components for the Patriot missile system).
But supply-chain bottlenecks remain — shortages in high-end seekers and other subsystems mean that deliveries might lag strategic ambitions. If Southeast Asian partners expect rapid ‘plug-and-play’ upgrades, they may be disappointed.
Institutional and governance challenges: hardware deliveries alone won’t shift the balance of power. If radar systems arrive without integration into broader networks, or boats arrive without sustainable logistics and trained crews, then the strategic dividend is modest. Southeast Asian states must invest in governance, training, interoperability — or else Japan’s hardware may overwhelm local absorptive capacity.
The heart of the matter lies in the strategic posture of ASEAN: Over decades, Southeast Asian states have maintained a hedging strategy by cultivating ties with all major powers (China, the U.S., Japan), avoiding formal alliances, and drawing resources from competing patrons. This approach — sometimes termed “omni‐enmeshment” — underpins ASEAN’s centrality in regional diplomacy. But Tokyo’s transition complicates that framework.
Japan’s trajectory is largely shaped externally (by its alliance with the U.S., by regional threat perceptions) and internally (by its budgetary and industrial ambitions) — ASEAN as a collective institution has only limited capacity to shape Japan’s role. The real decisions are being made by national capitals, each with its own calculus: the Philippines, Vietnam, Indonesia, Malaysia, Singapore all see different risks and opportunities.
For instance, the Philippines has embraced Japan’s security cooperation relatively openly; Vietnam welcomes capacity-building but remains cautious about binding defence alliances; Indonesia and Malaysia prefer to keep deeper enough distance. This divergence underscores why ASEAN as a bloc cannot easily coordinate a unified response to Japan’s shift.
The proper framing may not be ASEAN trying to steer Japan entirely. Instead, Southeast Asian states must steer their cooperation with Japan — individually or in minilaterals — so that Tokyo’s capabilities produce public-good benefits rather than simply aligning with U.S. alliance logic.
Focus cooperation in areas of shared interest: maritime domain awareness, coast-guard support, radar and sensor networks, search-and-rescue, humanitarian assistance/disaster relief (HADR) — these are less provocative than heavy naval strike platforms yet deliver tangible sovereignty gains.
Embed Japan-led or Japan-supported projects in ASEAN frameworks or U.N. mechanisms, so that the domestic politics of Southeast Asian states can frame involvement as regional rather than purely external.
Prioritise governance and logistic readiness: ensure that hardware delivered is matched by crew training, logistics systems, interoperability standards, and data-sharing protocols.
Maintain flexibility: Southeast Asian states must maintain ties to China and other regional powers even as they deepen cooperation with Japan; the objective is not to join a new bloc but to stay hedged.
Monitor the domestic industrial capacity of Japan: understand lead-times, supply-chain risks, and manage expectations so that cooperation is realistic rather than aspirational.
The Philippines. Manila has been among the earliest to capitalise on Tokyo’s new security outreach. The signing of a Reciprocal Access Agreement (RAA) with Japan enables Japanese Self-Defence Forces and Philippine forces to conduct joint exercises, access bases, and coordinate logistics. While direct Japanese commentary is limited publicly, analysts note the significance of this step for Manila’s deterrence calculus vis-à-vis China. This cooperative dynamic underscores how Japan is moving from being a passive partner to an active security provider in Southeast Asia.
Vietnam. Hanoi has taken a parallel but more measured path. The JICA-loan for coast-guard vessels reflects trust in Japan’s capacity-building narrative. Vietnam remains conscious of its delicate relationship with China and therefore limits formal alliance commitments. Still, the Japanese capacity-building avenue offers a complementary path for Vietnamese maritime enforcement and domain awareness without overt alliance entanglement.
Indonesia and Malaysia. These two states exemplify the tighter balancing act. Both face Chinese maritime coercion, but both also have deep economic links with China (trade, investment, infrastructure). Japan’s enhanced security role complicates neutrality. Should Tokyo’s posture widen into operational presence or forward basing, Indonesia and Malaysia may feel increased pressure to choose sides — something they have long avoided through hedging.
ASEAN as institution. While ASEAN continues to convene major-power dialogues, promote a rules-based order, and seek maritime governance cooperation (e.g., the Code of Conduct in the South China Sea), its capacity to shape Japan’s strategic trajectory is weak. For many member states, the decision rests in national capitals, not at ASEAN summit tables.
The shift in Japan’s posture matters beyond Southeast Asia. Several broader implications are worth noting:
U.S.–Japan Alliance Rebalanced. Japan’s new strategy gives the alliance more depth and burden-sharing capacity. Some analysts argue that Japan is moving from “ally support” to “deterrent actor” in its own right.
China’s Strategic Calculus. Japan’s faster defence buildup and broader regional posture will force Beijing to reassess its maritime and aerial operations — both in Japanese approaches and via Southeast Asian responses. For China, cooperation between Japan and ASEAN might be less threatening than Japan aligning operationally with U.S. forward posture; but either way it raises the risk of mis-calculations.
Maritime Domain Greater Emphasis. The Japanese focus on radars, surveillance, long-range strike and integrated multi-domain operations means that maritime enforcement and domain awareness in the South China Sea, Sulu-Celebes Sea and adjacent zones will change. Southeast Asian coastal states stand to gain capacity but also enter into more complex security webs.
Arms Export and Industrial Network Effects. Japan relaxing its arms-export restrictions (which only in recent years were significantly loosened) opens the possibility of Japanese defence industry becoming more actively integrated with regional partners. But as noted, bottlenecks remain.
Hedging No Longer Passive. For Southeast Asian states, hedging is no longer about sitting equidistant. It is about actively shaping how external powers deploy in and around them. Japan’s rise means that if Southeast Asia sleeps, it may wake to a strategic order largely pre-defined by Japan-U.S. logic rather than by ASEAN agency.
This new era comes with real dangers. If mismanaged, Japan’s rearmament could undermine regional stability rather than bolster it.
Chinese Retaliation. States that publicly deepen cooperation with Japan risk diplomatic or economic backlash from Beijing. Even if the cooperation is ostensibly non-aligned, the optics matter.
Supply-chain & Delivery Delays. As mentioned, Japan’s ambition may outstrip its industrial capacity in the short to medium term. That exposes Southeast Asian partners to the risk of stranded capability — promised radars, boats or missile systems may arrive late or at reduced scale.
Governance Gap. Hardware is only half the story. Without trained crews, maintenance systems and integration into broader command-and-control, platforms delivered may sit idle or deliver marginal strategic benefit.
Escalation Spiral. If Japan’s increasing role is perceived by China (or by regional actors) as a stepping-stone to a new containment bloc, the security dynamics could shift from deterrence to dynamic escalation. Southeast Asian states may then be forced into harder choices.
Blurring of Alliance Lines. While Japan frames many of its engagements in cooperative, non-alliance terms, the underlying alignment with U.S. strategy is substantial. ASEAN states that hope to stay firmly neutral may find the choice less clear-cut than before — and may lose leverage as a result.
Given this set of dynamics, what can Southeast Asian states realistically do? Here are some pragmatic strategic priorities:
Define Japan’s role on regional terms. Rather than accept Japan’s outreach as a fait accompli, Southeast Asian states should engage Tokyo to define cooperation in areas that serve Southeast Asian institutional interests (maritime governance, coast-guard interoperability, disaster relief) rather than purely military strike‐capabilities.
Embed projects within multilateral frameworks. Whenever possible, structure Japan–Southeast Asia cooperation through ASEAN, the U.N., or other multilateral vehicles. That helps diffuse the optics of bloc alignment and retains ASEAN’s convening role.
Invest in absorptive capacity. National governments should ensure that any hardware or capability partnership comes with matching investment in training, maintenance, data-integration and doctrine. Without this, the capability is fragile.
Maintain hedging flexibility. Deepening one set of partnerships (with Japan) need not mean severing others (with China, or other regional actors). Southeast Asian states should retain diverse ties — economic, diplomatic, security — so that Japan is a partner of choice rather than the only partner.
Monitor Japanese industrial and delivery timelines. Stay realistic about what Japan can deliver when. Avoid strategic surprises born of over-expectation.
Lead the narrative. Recognise that Japan’s rise will be integrated into bigger regional frames — the U.S. alliance system, Indo-Pacific strategy, etc. Southeast Asian states need to assert narrative agency: that this is their region and their sovereignty they are balancing.
In 2025, hedging is no longer a passive posture. It is an active strategy. It is about shaping external powers rather than simply being shaped by them. The recalibration of Japan’s defence posture raises the question: will Southeast Asia be a platform for Tokyo (and by extension Washington) — or will these states become co-authors of a new maritime order?
If Southeast Asian states coordinate effectively — whether bilaterally with Tokyo, in minilaterals (e.g., Japan-Philippines-Vietnam) or through selective ASEAN frameworks — then Japan’s rearmament could translate into a maritime governance dividend: better domain awareness, improved enforcement of sovereign rights, and a stronger regional deterrent against coercion.
If not, then Japan’s trajectory may simply be subsumed into a wider U.S. strategy, leaving Southeast Asia as spectator rather than shaper. The cost of inaction would be steep: fewer options, more constraint, and an external order largely written elsewhere.
Japan’s new role does not automatically spell confrontation. Indeed, a more capable Japan can become a provider of regional public goods — patrol assets, domain-awareness networks, logistics hubs — if Southeast Asian states help define the terms of engagement. But the alternative is drift — Tokyo’s rearmament absorbed into great-power dynamics, leaving Southeast Asia’s interests marginalised.
