In 1893, a few decades after the first transatlantic cable was laid, Rudyard Kipling published a poem about the marvels of “The Deep-Sea Cables.” As communication became nearly instantaneous, Kipling heralded the connectivity that was previously unimaginable, writing, “Let us be one!”

Over a century later, telegraph lines have given way to fiber-optic cables, but their unifying promise has all but faded. The seabed has become an arena of great-power competition, sabotage, and surveillance. Fiber-optic data cables carry 99 percent of transoceanic digital traffic, including financial flows and government, diplomatic, and military communications. But as risks grow and trust erodes, global cabling is splintering into U.S.-led, Chinese-led, and nonaligned blocs, with routes and landings increasingly mirroring geopolitical alignment rather than commercial logic.

The vulnerabilities of critical subsea infrastructure are especially pronounced in Europe. The September 2022 Nord Stream pipeline explosions in the Baltic Sea drew global attention to these risks. Subsequent incidents in the Baltic, including damage investigators traced to a Chinese-linked vessel, showed how actors from one region can endanger infrastructure in another. Increased vessel and submarine activity along Atlantic and Baltic routes has also heightened concerns about undersea surveillance, as adversaries map and monitor critical cable routes.

Asia faces similar risks, even if they attract less attention. Taiwan reports seven to eight cable breaks annually, with most linked to China—part of Beijing’s broader coercive campaign against the island. In March, Beijing unveiled a deep-sea cable cutter that is reportedly compatible with uncrewed submersibles and capable of severing cables at depths of more than 13,000 feet—twice the operational depth of subsea communication systems. But even as incidents become more frequent and the capacity for interference grows, states have a hard time attributing cable cuts to particular actors and holding those ultimately responsible to account.

These dangers are compounded by an overlooked bureaucratic challenge: the use of legal and regulatory pressure to deny, delay, or complicate cable surveys, installation, and repairs. In the South China Sea, such tactics have helped China expand its de facto control over the seabed. Some companies are rerouting cables around disputed areas rather than contesting China’s claims.

Despite the growing importance of subsea cables, the laws and institutions governing them have not kept pace. The relevant provisions of the 1982 UN Convention on the Law of the Sea (UNCLOS) were drafted for an earlier era and build on the 1884 Convention for the Protection of Submarine Telegraph Cables, which was signed by the monarchs of Kipling’s time. Securing the world’s subsea arteries demands a comprehensive global architecture that links national and regional efforts with international ones and modernizes the legal and institutional regime.

The United States is uniquely positioned to lead this effort. Although it has challenged China’s attempts to dominate the waters of the South China Sea by conducting freedom of navigation operations, the United States has largely ceded the sea floor. If this neglect continues, Washington risks losing control not only of communications and energy lifelines beneath the waters but the balance of power above.

UNCLOS guarantees certain basic freedoms. A coastal state enjoys sovereignty in its 12-nautical-mile territorial sea. But beyond that limit, all states have the freedom to lay, maintain, and repair cables, including in exclusive economic zones and on continental shelves—the submerged extension of a country’s land territory. The convention explicitly protects the laying and maintenance of cables on continental shelves and stipulates that coastal states “may not impede” these activities, subject to “reasonable measures” for resource development and pollution control. Although the United States is not a party to UNCLOS, it treats the convention’s provisions on subsea cables as reflecting customary international law, and they serve as the authoritative codification of cable-related rules alongside the narrower 1884 Convention, which remains the formal treaty instrument for nonparties.

Domestic implementation of UNCLOS, however, does not always conform to the convention’s requirements. For example, although China ratified UNCLOS in 1996, its 1989 Provisions Governing the Laying of Submarine Cables and Pipelines directly contradict the convention by requiring foreign companies to secure consent for cable routes across its continental shelf, as well as for maintenance or repair.

The legal framework governing subsea cables also suffers from structural flaws. Countries often struggle to hold perpetrators to account for deliberate damage to subsea cables given jurisdictional limits in UNCLOS, weak flag state enforcement, and difficulties attributing incidents to actors. If incidents occur beyond the territorial waters of a coastal state, then only the country in which a suspected ship is registered—the flag state—has jurisdiction to investigate and prosecute any actors suspected of causing damage to cables. But many commercial vessels are registered in regimes that lack the will or the capacity to act. This was brought into sharp relief in October, when a Finnish court dismissed sabotage charges against the crew of the Eagle S, a Russian-linked tanker suspected of severing five critical Baltic cables, on jurisdictional grounds because the incident........

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