U.S.–China Naval Tensions in the Contested Waters of Southeast Asia: An Explainer (2025)
Tensions between the United States and China in the contested waters of Southeast Asia remain one of the most pressing security issues in the Indo-Pacific region. With overlapping maritime claims involving China, Vietnam, the Philippines, Malaysia, Brunei, and Taiwan, the area has become a flashpoint where freedom of navigation, sovereignty disputes, and great-power competition intersect.
Why the Waters Are Disputed
The contested waters of Southeast Asia are rich in natural resources and serve as one of the world’s busiest shipping lanes. More than one-third of global maritime trade passes through these waters each year. China claims nearly the entire area under its so-called “nine-dash line,” a claim rejected by an international tribunal ruling in 2016. Other coastal states—including Vietnam, the Philippines, Malaysia, and Brunei—assert sovereignty over parts of the region, while Taiwan maintains similar claims to Beijing.
The U.S. Role and Naval Operations
The United States does not take a position on sovereignty disputes but insists on freedom of navigation under international law, particularly the United Nations Convention on the Law of the Sea (UNCLOS). To uphold these principles, the U.S. Navy regularly conducts Freedom of Navigation Operations (FONOPs). These missions challenge what Washington views as excessive maritime claims, including China’s militarization of artificial islands.
China, however, views U.S. patrols as provocations and often dispatches warships or aircraft to shadow and warn U.S. vessels. This pattern has created a cycle of military signaling, with each side demonstrating resolve without triggering direct conflict.
Flashpoints in 2025
In 2025, the contested waters of Southeast Asia remain tense but below the threshold of open conflict. Several recent developments highlight the risks:
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Near Misses at Sea: Encounters between Chinese vessels and U.S. or allied ships have grown more frequent. In some cases, Chinese warships maneuvered dangerously close to U.S. destroyers, raising fears of accidental collisions.
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Increased Military Presence: China continues to fortify its artificial islands with runways, missile systems, and radar installations. The U.S., meanwhile, has increased rotational deployments through the Philippines under the Enhanced Defense Cooperation Agreement (EDCA).
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Regional Pushback: Southeast Asian nations are diversifying security partnerships. The Philippines has deepened ties with both the U.S. and Japan, while Vietnam is strengthening defense dialogues with India, Australia, and European partners.
Risks of Escalation
Military analysts warn that while both Washington and Beijing wish to avoid war, the risk of miscalculation is high. Naval and aerial encounters occur in close quarters, and without strong communication channels, even a minor accident could spiral into a crisis.
The contested waters of Southeast Asia are also closely tied to broader U.S.–China competition over technology, trade, and regional influence. This means maritime disputes are not just about borders—they are about the balance of power in Asia.
What to Watch
As of mid-2025, three key dynamics will shape the trajectory of U.S.–China tensions:
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U.S. Commitment to Alliances: Washington’s ability to reassure allies like the Philippines and Japan will determine whether the U.S. presence is seen as stabilizing or escalatory.
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China’s Assertiveness: Beijing shows no sign of backing down from its expansive claims, and its military modernization continues at a rapid pace.
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Regional Diplomacy: ASEAN countries are seeking a Code of Conduct with China, but progress has been slow. Whether diplomacy can reduce risks remains an open question.
Conclusion
The contested waters of Southeast Asia have become a strategic crossroads where great-power rivalry and local sovereignty disputes collide. For the U.S., the issue is about defending freedom of navigation and supporting allies. For China, it is about asserting historical claims and expanding regional influence.
As tensions persist in 2025, the challenge for all parties is preventing incidents at sea from escalating into wider conflict. While diplomacy offers some hope, the reality is that the region will likely remain a hotspot for years to come.