The South China Sea looks like a tongue hanging down from the Chinese mainland to its north. Vietnam lies to the west, Malaysia to the south, the Philippines and Taiwan to the east. Rocks, shoals, reefs, and islands dot the sea. Fisheries abound, oil gurgles beneath the seabed. The countries that line its coasts all hunger for these resources. But they disagree over who owns what.

Lately the temperature is rising in these decades-old conflicts. Last week, Vietnamsignaled that it might join the Philippines in a legal action against China. Vietnam wants to stop China from exploring for oil in a part of the South China Sea that Vietnam claims for itself, while the Philippines is smarting over China’s eviction of Philippine fishermen from traditional fishing grounds back in 2012.

Both Vietnam and the Philippines have strong claims, and so it might seem reasonable for them to seek arbitration. But a tribunal can’t stop China from bullying its neighbors. The countries can halt Chinese expansion into the South China Sea only if the United States backs them up, and it is unlikely that the United States will. Over the long run, it can’t.

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