Southeast Asia Defense: Beyond US Influence & Security

Southeast Asia faces increasing uncertainty as the reliability of American security assurances diminishes, particularly as the possibility of a crisis involving Taiwan grows. The region will likely be impacted by the operational and political pressures of great-power conflict regardless of its diplomatic choices.

China’s Focus on Taiwan and Southeast Asia

China is observing U.S. responses in Iran and Ukraine for indications of hesitation before potentially acting regarding Taiwan. The People’s Liberation Army (PLA) views Southeast Asia as crucial to any Taiwan contingency, tasking its Southern Theatre Command with securing its southern flank. Southeast Asian nations will face operational demands, including decisions about airspace and water access, and sustaining defense partnerships, regardless of their diplomatic stances.

Limited Regional Preparedness

Recent simulation exercises conducted by the International Institute for Strategic Studies suggest that many regional governments primarily view a Taiwan contingency as a logistical issue – specifically, citizen evacuation – without fully considering the broader implications. Planning continues to rely on external support from either China or the United States, assuming the crisis ends once civilians are moved.

A crisis in the Taiwan Strait would extend beyond evacuation efforts. Following civilian removal, Southeast Asian states will confront strategic decisions regarding access, basing arrangements, and support for external operations under pressure. These are not logistical concerns, but strategic ones, requiring states to position themselves within the crisis, with no single option – alignment with the U.S. or China, or neutrality – offering guaranteed protection.

Erosion of U.S. Commitments and Limited Alternatives

Domestic factors in the U.S. have weakened support for long-term global deployments, increasing pressure for conditional burden-sharing. The U.S. also retains the ability to impose costs on allies that align too closely with Beijing, leaving Southeast Asia vulnerable to both abandonment and coercion. Other powers are unlikely to fill the security gap; Japan will prioritize crises closer to home, particularly Taiwan, while India focuses on its disputes with China and Pakistan and the western Indian Ocean.

Deferring to China’s position on Taiwan does not resolve the challenges facing the region. While it may avoid immediate confrontation, it does not guarantee protection if the military balance shifts. Neutrality also fails to address the spillover pressures from a Taiwan contingency, as it cannot be enforced without the capacity to deny external access and resist coercion.

Rethinking Regional Defense

Defense planning across Southeast Asia remains largely inward-focused, concentrating on immediate threats and neighboring countries. Anti-access/area-denial strategies are unevenly developed and often shaped by internal security concerns rather than external defense requirements, with limited integration at regional levels.

A new approach is needed, one that reconsiders how defense is understood, moving beyond purely national terms to encompass the wider regional space. This does not necessitate collective action or new institutions, but rather independent assessments by each state of how its capabilities relate to the regional geography.

Specifically, this involves:

• Mapping key avenues of advance for external powers.
• Identifying key terrain, chokepoints, and vulnerabilities.
• Concentrating efforts on positions each state can credibly hold without compromising its immediate defenses.

States should contribute based on calculation, recognizing that instability can reduce strategic depth and expose defensive lines. Rather than dispersing forces, each state should identify key positions for defense while maintaining the ability to maneuver. This approach does not eliminate the choice between alignment and neutrality, but it allows states to manage spillover pressures and avoid having operational necessities dictate alignment outcomes.

A Taiwan contingency will inevitably impact Southeast Asia, presenting the same operational demands regardless of alignment. The critical question is whether these positions can be sustained under pressure, or whether foreign policy will become reactive rather than strategic.