Hooroo, China! Australian Prime Minister Anthony Albanese is evidently making good on an election campaign pledge to reclaim the Port of Darwin, a harbor in Australia’s Northern Territory, from Chinese control. The Chinese firm Landbridge has operated the port since 2015 under a 99-year lease. Last week the American private-equity firm Cerberus voiced interest in leasing the port from Canberra. Albanese cited national security grounds for breaking the lease.

    Why does Chinese control over Darwin’s port matter? First and foremost, Darwin occupies prime real estate. Maritime historian Alfred Thayer Mahan fashioned a trio of metrics to help naval officialdom judge the worth of any strategic position, chiefly candidate sites for naval bases. “Situation,” or geographic position, meant a site’s proximity to something naval commanders wanted to influence—a hostile base, an important seacoast, or a strategic waterway. “Strength” connoted some combination of natural and manmade defenses to hold enemies at bay. “Resources” referred to the port’s or surrounding countryside’s ability to furnish warships with fuel, ammunition, and stores of all types.

    Darwin measures up handily by Mahanian standards in all three metrics—strategic position in particular. It is Australia’s northernmost major harbor, situated along an outcropping of land jutting toward the rim of the South China Sea. Maritime forces stationed there enjoy a central position just outside the southerly arc of Asia’s first island chain, which meanders from Japan through Taiwan, the Philippine Islands, and the Indonesian archipelago before terminating at the Strait of Malacca. Of particular note, the Sunda and Lombok straits, the best alternative passages to Malacca, lie within reach of Darwin.

    Darwin Port’s fortunate position affords ships and aircraft liberty of horizontal movement. They can range from side to side on the map, helping seal off the first island chain to Chinese maritime and air movement. They also enjoy vertical access to the South China Sea, one of Asia’s and the world’s most embattled expanses. Small wonder, then, that some 2,500 US Marines from the I Marine Expeditionary Force now rotate through the port on an annual basis. Among other functions, these Marines are honing tactics for access denial while helping beleaguered allies like the Philippines uphold their nautical rights in the face of Chinese gray-zone aggression. On occasion, Darwin has also played host to US Navy attack submarines. Just this March, for instance, the attack boat USS Minnesota, accompanied by submarine tender Emory S. Land, put into the harbor for a port call.

    In short, Darwin occupies a strategic position of great price while boasting resources adequate to support seagoing forces. Leaving the port in Chinese hands would bestow on Beijing a golden opportunity to make mischief for Australia and its allies. At a bare minimum, Chinese observers could gather intelligence on Australian Defense Force and allied comings and goings while abetting net assessment of allied capabilities, tactics, techniques, and procedures. In so doing, they help acquaint the People’s Liberation Army (PLA) with potential foes, the first step toward defeating them. Nor is it farfetched to imagine Chinese port operators slow-rolling—or, more likely, actively hampering—allied military movements and resupply in wartime.

    Bear in mind that there is no such thing as an apolitical agreement with a Chinese company. Politics permeates everything in China; politics is warfare without bloodshed for the Chinese Communist Party; and domestic law obliges all Chinese firms, state-owned or not, to comply with party mandates on matters relating to national security. In other words, businesses constitute a geopolitical cudgel for Beijing as surely as the PLA does. And the party wields that weapon with zest on a 24/7/365 basis.

    So, kudos to Prime Minister Albanese for reasserting friendly dominion over Darwin Port.

    Not all maritime positions are created equal, as the Mahanian formula for gauging their value indicates. For instance, Darwin is less geopolitically pivotal than the Panama Canal, whose Pacific and Caribbean terminuses were, until recently, operated by the Hong Kong-based conglomerate CK Hutchison Holding. Last winter, the Trump administration successfully pressured the Hong Kong firm to transfer the leases to a consortium including BlackRock Inc. If the Panamanian government approves the transaction—it remains in limbo for the time being—the strategically situated waterway will, in effect, come under American control.

    That matters because of a fourth index of a strategic position’s value that Mahan did not explicitly incorporate into his formula—namely, alternatives. If there is no alternative to a position, it commands peerless value. Hawai’i, which sits alone in the vacant Eastern Pacific, is one such site.

    There are relatively accessible alternatives to Darwin for Australia-based forces, though none so convenient for coping with today’s strategic seascape. The only alternatives to the Panama Canal for the United States are the Northwest Passage, skirting the Arctic flanks of Alaska and Canada, or around Cape Horn, circumnavigating South America. But the Northwest Passage route is largely impractical for naval maneuver, while the Cape Horn passage is slow, burdensome, and weather-beaten. Both routes encumber strategic mobility.

    Geopolitics maven Nicholas Spykman observed that digging the Panama Canal in effect rewrote Western Hemisphere maritime geography. In practical terms, by sparing merchantmen and ships of war the long voyage around South America, artificially modifying geography teleported American east-coast ports thousands of miles closer to East Asia. Traders could now compete with European rivals on a more equal footing because merchant ships’ journeys to Pacific trading partners were comparable in length and duration. Just as important, the US Navy could swing forces from side to side through the Caribbean Sea, concentrating and reconcentrating fleets in whichever ocean the leadership deemed most in need.

    If it persists, Chinese control of the canal threatens to repeal Spykman’s geographical revolution. Like Anthony Albanese, Donald Trump was wise to usher China away from crucial marine geography. Here’s hoping fellow leaders around the world follow suit, rethinking Chinese control of their seaports. After all, Mahan depicts sea power as a “chain” connecting domestic manufacturing—via domestic seaports—with foreign harbors across the sea. Economic prosperity and martial prowess depend on ports. A country that cedes control of its ports to China grants Beijing the option to snap its sea-power chain. Deliberately empowering an antagonist in this way courts ruin. 

    Don’t let China break the chain.