Elizabeth Shackelford

The South China Sea has become one of the world’s most dangerous potential flashpoints. Territorial disputes in this area — often over uninhabitable rocks — have been a source of conflict and competing claims for a century. But China has become more aggressive recently with its claims to the area. With great power competition heating up worldwide, this could translate to big trouble.

In June, Chinese coast guard ships rammed and boarded Philippine navy vessels, using machetes, axes, and hammers to damage the boats and threaten the crews. It was the latest and most violent in a series of confrontations between China and the Philippines in the area.

At the core of the clash was Second Thomas Shoal, a submerged reef in the Spratly Islands, a little more than 100 nautical miles west of the Philippines, where the Philippine navy has maintained a presence with a handful of marines on a grounded Navy transport ship since 1999. The Philippine vessels were attacked as they were resupplying the outpost.

Why such violence over a rocky feature that doesn’t even qualify as land? For the Philippines, it’s a matter of sovereignty and standing up to the Chinese government’s overreach. Under international law, this shoal falls well within the Philippines’ exclusive economic zone.

For many others, including the United States, China’s aggressive claim to Second Thomas Shoal is part of a bigger threat to freedom of navigation in critical shipping lanes and to accessing a wealth of natural resources, from massive oil and natural gas reserves to abundant fish and seafood.

Several countries in the region lay claim to some of the islands, rocks and territorial waters of the South China Sea, but China’s claims are the most sweeping by far. They are demonstrated by the nine-dash line first detailed in a map China issued in 1947, which encompasses nearly the entirety of the sea, in an awkward U-shape stretching far south of China’s shores.

The nine-dash line is such a source of angst that Vietnam banned last year’s blockbuster movie “Barbie” because it portrays a childlike map that appears to show a dotted trail extending into the ocean from where China would be on the Asian landmass.

China has tried to strengthen its claim by expanding the size of islands it physically controls and by building new islands and militarizing them.

By the 1990s, China expanded its claims beyond islands and rocks to include the water itself, the seabed below and the airspace above. This is in clear violation of the 1982 Law of the Sea Convention — a treaty that China not only signed but also helped negotiate.

The shipping lanes mean these local skirmishes have global implications, and potentially global responses, since more than 20% of all global trade and 60% of maritime trade pass through these waters. A meaningful threat to the global economy doesn’t stay local for long.

This is a big part of America’s interest in maintaining peace and security in the region. Freedom of navigation is one of the oldest principles of international law, going back 400 years. The United States has made the defense of freedom of navigation worldwide a core U.S. national security priority.

But an even riskier element comes from U.S. security commitments in the region — one in particular. The United States engages in defense cooperation with Vietnam, but has no clear commitments to come to its defense. The U.S. government has enshrined into law its commitment to assist Taiwan in case of an attack, but the nature of how we would do so remains intentionally ambiguous.

The Philippines, however, is a treaty ally with whom we’ve clearly agreed to mutual defense. This means that an armed attack on the Philippines would invoke America’s commitment to defend it. If that attack comes from China, the United States could quickly find itself in direct conflict with a near-peer global power.

For decades, it wasn’t at all clear how the Philippines’ claims to these disputed islands factored into that commitment. This suited the U.S. government, since ambiguity was a deterrent to any provocations by the Philippines against China’s competing claims.

But that all changed in 2019, when then-Secretary of State Mike Pompeo stated publicly that the islands were included in that pact. Today, U.S. government guidelines make clear that the commitment applies to Philippines assets anywhere within the South China Sea.

The good news is that the United States and its partners in the region are eager, so far, to avoid full-scale war. Since the most recent skirmish, Philippine President Ferdinand Marcos Jr. has publicly stated that his country is “not in the business to instigate wars,” and his government indicated that it would not invoke its treaty with the United States over the incident.

Avoiding war with China, though, requires the Philippines and its Western ally to strike the right balance by not escalating tensions with China but also not emboldening it to go further.

It will also depend on how keen China is to avoid war, and given its recent actions, that might not be a shared priority.

Elizabeth Shackelford is the Magro Family Distinguished Visitor in International Affairs at Dartmouth College and a foreign affairs columnist for the Chicago Tribune. She was previously a U.S. diplomat and is the author of “The Dissent Channel: American Diplomacy in a Dishonest Age.”