The Associated Press recently posed a pointed question: why does the United States keep treating Taiwan's security and the South China Sea's security as bound together? Hunter Marston, who directs the Southeast Asia program at Australia's Lowy Institute, argued the two are "closely linked": if Beijing blockaded or seized Taiwan by force, the shock would likely spill quickly into the South China Sea, and if China gained control of Taiwan, or if Washington ever declared outright that it would not come to Taiwan's defense, Beijing would also gain far greater freedom to project military power, submarines especially, beyond the first island chain.
That framing captures something real, but it should not be flattened into "if Taiwan falls, China controls the South China Sea." The two seas function as twin gateways of a single operational system, not as two bombs wired to explode the instant either one is touched. A more precise way to put it: this is one theater of war, but the two flashpoints run on different fuses.
Control Of Taiwan Would Shift Costs Not Hand Over Sea Power
Taiwan sits at the junction of the East China Sea, the South China Sea and the Philippine Sea, and the Luzon Strait to its south, which includes the Bashi Channel, is a vital passage for Chinese vessels moving from the South China Sea into the western Pacific. Beijing already operates a nuclear submarine base on Hainan and has built runways, radar and port facilities on artificial islands in the Spratlys, and Chinese carrier groups have already transited the Bashi and Miyako channels on multiple occasions. Seizing Taiwan, in other words, would not represent the People's Liberation Army's first breakout beyond the island chain.
What would genuinely change is that Beijing could convert Taiwan's east coast into a sensing, aviation, missile and logistics node facing the deep water Pacific, shortening the distance some of its forces need to travel to reach the Philippine Sea and complicating anti submarine warfare, early warning and reinforcement efforts by the United States, Japan and the Philippines. The Pentagon's 2025 China Military Power Report likewise noted that the Southern Theater Command, which oversees the South China Sea, would support the Eastern Theater Command in a Taiwan contingency. The South China Sea would therefore not simply be a shipping lane caught in the crossfire, but potentially a second theater shaped by Hainan's submarine fleet, Southern Theater forces and the interplay of American and Philippine bases.
Sea denial, however, is not the same as sea control. Taiwan's eastern ports have limited capacity, any new base would take years to build, and both would remain vulnerable to mines, long range strikes and anti submarine blockades, while allied surveillance lines could still be rebuilt along a chain running from the southern Ryukyus to Luzon. Taking Taiwan would improve Beijing's cost structure, operational depth and staying power, but it would not erase in one stroke the counter measures available to American submarines, Japan's southwestern islands or bases in northern Philippines. Geography matters enormously here, but it is not an irreversible verdict.
The Bases Are Already Linked The Treaties Are Not
The nine sites under the US Philippines Enhanced Defense Cooperation Agreement have already drawn an operational line connecting the two seas. Among the newer additions, two sites in Cagayan and one in Isabela sit in northern Luzon, close to Taiwan and the Bashi Channel, while a site on Balabac Island faces the South China Sea. The 2026 Balikatan exercises rehearsed maritime strikes near the Batanes Islands, close to Taiwan, while simultaneously practicing anti landing operations in Zambales, which faces the South China Sea. From coastal missile deployments to dispersed basing to logistics planning, American military planners have stopped treating the two seas as separate maps.
That operational integration, though, should not be mistaken for automatic alliance intervention. The Taiwan Relations Act obligates the United States to provide Taiwan with defensive arms and to maintain the capacity to resist force or coercion, but it contains no NATO style automatic entry clause. The US Philippines Mutual Defense Treaty covers Philippine forces, public vessels and aircraft attacked in the South China Sea, yet whether any given incident meets the threshold of an "armed attack," and how Washington would respond, still runs through a constitutional process. The US Japan security treaty, meanwhile, directly guarantees only territory under Japanese administration, not Taiwan.
The real danger lies in how a crisis could pull different fuses in sequence: fighting over Taiwan would turn the Bashi Channel and northern Luzon into reinforcement, interdiction and evacuation nodes; if American forces then used Philippine facilities, Beijing might widen its strikes; and only if Philippine forces or bases themselves came under attack would the US Philippines treaty likely be invoked. This is not dominoes falling on their own, but an escalation chain driven by military necessity and accelerated, at each step, by political decisions.
Markets Will React Before Alliances Do
Economic spillover typically outruns treaty responses. Using 2024 data, the Center for Strategic and International Studies estimated that the Taiwan Strait and the Malacca Strait each carry more than 2.4 trillion dollars in goods, each accounting for roughly a fifth of global maritime trade. Because some of that cargo overlaps between the two routes, the figures cannot simply be added together as a combined loss, and ships can still reroute east of Taiwan, so closing the Taiwan Strait would not cut off the world entirely. But rerouting means missing existing port networks, which drives up shipping schedules, fuel costs, inventory, insurance and financing costs.
Harder still to replace is semiconductor output. Taiwan accounts for more than 60 percent of global foundry revenue and over 90 percent of the world's most advanced chip manufacturing capacity. The Rhodium Group has estimated that a blockade scenario alone could put more than 2 trillion dollars of economic activity at risk of disruption, a measure of exposure rather than a guaranteed loss of output, but enough to show that markets will not wait for the first missile to fly. Once insurers, shipowners and banks conclude that a risk cannot be priced, they tend to pull back on coverage, reroute cargo, stockpile inventory and tighten credit well before any shot is fired.
Washington Has Interests There Not Unlimited Resources
Washington's stake in the region is not solely about defending Taiwan. It is about preventing any single power from dominating the first island chain, and about preserving the security of allies such as Japan and the Philippines, along with technology supply chains and international shipping lanes. But having clear interests is not the same as having unlimited capability. The recent redeployment of Western Pacific carriers toward the Middle East is a reminder that the Indo Pacific competes with other theaters for the same ships, aircraft, munitions and political attention.
By the same token, if the United States were to publicly rule out defending Taiwan, that would not overnight increase the People's Liberation Army's missile range or submarine numbers, but it would lower Beijing's estimate of the cost of intervention, forcing Japan and the Philippines to reassess their own rearmament, base access arrangements and hedging strategies toward China. That is a spillover in credibility, not a magic multiplier of firepower.
For Taiwan, two misreadings stand out as especially dangerous: believing that any crisis over Taiwan is automatically the whole world's crisis, guaranteeing that allies will fight, and treating the South China Sea as purely a Southeast Asian dispute with no bearing on Taiwan's own defense. The first overestimates what treaties promise. The second underestimates what geography dictates.
Taipei's task is to turn this abstract linkage into preparations that can actually be verified: building maritime surveillance and anti submarine early warning exchanges with Japan and the Philippines, pre coordinating evacuation, search and rescue, port diversion, undersea cable repair and medical transport, establishing public war risk insurance along with emergency shipping and energy backup plans, and clarifying in advance the thresholds for base access, gray zone activity and armed attack so that no side escalates based purely on worst case assumptions.
If the Taiwan Strait falls, the consequences will not stop at Taiwan's own coastline, and if the South China Sea spins out of control, the pressure will travel north along energy and shipping routes as well. But a chain of linked risks is not the same thing as war being inevitable. The most effective deterrence does not rest on declaring that every country will automatically fight for Taiwan. It rests on making sure Beijing understands that altering the status quo in the Taiwan Strait would simultaneously shake regional bases, alliance decision making, shipping markets and technology supply chains all at once, so that the cost can never be contained to one place. A single theater can sustain a shared deterrent. Different fuses still have to be wired together, through institutional coordination and through Taiwan's own capacity to defend itself.
The author holds a doctorate in international politics from Humboldt University of Berlin and is an associate professor in the Department of Public Affairs and Civic Education at National Changhua University of Education.
