In 1609 the Dutch jurist Hugo Grotius penned Mare Liberum (Freedom of the Seas), where he argued that the oceans should be a civilizational commons where anyone can travel for purposes of peaceful commerce. His goal was to offer an alternative vision to the mare clausum (closed sea) promulgated by the Portuguese, who sought to monopolize Indian trade to the economic disadvantage of the Netherlands. The idea of the oceans being open and freely navigable would, like so much of Grotius’s thought, live on long beyond his age. 

The mare liberum would be enforced by the naval might of the British Empire in the 19th and early 20th centuries, driving an era of increasing global connection, mutual commerce, and prosperity. Merchant vessels from across the world could ply their trade in exotic ports and the laying of undersea cables made communication exponentially faster than ever before. Even so, the idea of free seas was not uncontested; nations and non-state actors fought against this regnant maritime ideology, trying to close territorial waters, impede commercial rivals, or simply hijack goods for profit. These challenges could only be deterred by force, usually supplied by a sovereign state.

This linkage between commercial trade and the need for a protective navy is where modern navalist philosophy, perhaps best espoused by the American historian Alfred Thayer Mahan, came into being. In his seminal 1890 work, The Influence of Sea Power Upon History, Mahan laid out this connection:

The necessity of a navy, in the restricted sense of the word, springs, therefore, from the existence of a peaceful shipping, and disappears with it, except in the case of a nation which has aggressive tendencies, and keeps up a navy merely as a branch of the military establishment… [sea power is] not only the military strength afloat, that rules the sea or any part of it by force of arms, but also the peaceful commerce and shipping from which alone a military fleet naturally and healthfully springs, and on which it securely rests,…

Mahan’s ideas were deeply influential and, combined with the Grotian doctrine of mare liberum, encouraged the use of navies to protect commerce and keep global trade flowing through the 20th century. 

However, the idea of using naval power to secure peaceful trade – even beyond one’s own vessels – has a flip side: using naval power to coerce or deter the peaceful trade of others. We are seeing both sides of this coin in the current competition between the United States and China.

The United States has relied on sea power since its inception owing to its heavy dependence on seaborne exports and imports. Our shared maritime heritage with the United Kingdom allowed for the peaceful transfer of naval predominance after World War II, with the US picking up where the British Empire left off. Since 1945, the American navy has ensured the idea of mare liberum, backed by institutions of international law. This norm of the free sea, defended by the American navy, has made the modern world what it is: globalized, interconnected, and rich. It has also greatly benefited the United States. Now, after nearly 80 years, a serious challenge has arisen: the Chinese Communist Party.

The Chinese government does not view mare liberum as the ideal, instead seeking to exert its own control over the seas. It sees the current system of free oceanic trade as biased towards American interests and wishes to shift that balance in its favor. One of the primary ways it seeks to change the status quo is through occupying of the world’s waters and assertion of special rights based on this adverse possession. China looks to leverage its blue water naval strength as much as possible, building a presence around the most critical parts of the global sea lines of communication (SLOC), maritime choke points.

The Middle Kingdom has been steadily increasing its presence at these crucial areas, both in the Indo-Pacific and much further abroad. Combined with China’s modernized version of mare clausum, its coercive diplomacy, and its policy of civil-military fusion, this has the potential to be a serious problem. The Chinese Communist Party (CCP) uses its diplomatic heft aggressively, either cajoling nations into accepting its entreaties or roping them into predatory agreements. Its focus on dual-use infrastructure ensures that wherever Chinese state-owned enterprises (SOEs) go, its military apparatus will follow. Using these positions, Xi Jinping’s nation could – in times of conflict – restrict passage through key seas and straits, raid commercial vessels, conduct technological espionage, use cyberattacks to cripple critical infrastructure, and force its enemies to play defense on a grand scale.

The Maoist state is putting its plan into action most assertively in its near-abroad. It has militarized the South China Sea, claiming it as its sovereign territory contra international law, creating artificial islands on which to base military assets, and asserting undersea rights over submarine cables – the arteries of the information age. Its quest to conquer Taiwan fits this paradigm, as the island sits astride the Taiwan Strait, a passage through which a significant portion of global commerce travels. It has invested heavily in dual-use port infrastructure in Malaysia and Indonesia, nations which lie next to the Strait of Malacca, the key seaway between the Pacific and Indian Oceans and a lifeline for both China and India. The East Asian nation has invested in major port infrastructure in Sri Lanka and used its debt-based leverage to force Chinese naval access to these ports not far from India. In Oceania, the Chinese People’s Republic has built security relationships with several nations in a quest to isolate Australia.

Further afield, China has invested in port infrastructure at Gwadar in Pakistan, turning it into a hub for Chinese commerce and militarism; conveniently, Gwadar lies just past the exit of the Persian Gulf, one of the world’s most trafficked seas. Just up that waterway, China has built relationships with Iran and Saudi Arabia – including brokering a recent rapprochement between the Islamic powers – ensuring access to potential dual-use infrastructure in the region. Its first overseas military base is in Djibouti, giving China the potential to project power through the Red Sea and the vital Suez Canal at its northern terminus. 

The CCP has also extended its activities into the Western Hemisphere, focusing on strategic waterways in Latin America. It is working to create a naval base at Ushuaia in Argentina, across from the Falkland Islands and just above the southern passage from the Atlantic to the Pacific Ocean. It has also invested heavily in the Panama Canal zone, ringing that waterway with CCP-linked dual-use facilities. As a backup, it has promoted a rival passage through Nicaragua, one of its key allies in the region. Finally, China has asserted itself as an “Arctic nation,” seeking to gain a powerful maritime presence in this increasingly-important strategic realm.

This is not a minor challenge, but one which strikes at the heart of the world order and American sea power. China has already outbuilt us in terms of ships – both commercial and military – and seeks to put that primacy to use in its broader aim of displacing American hegemony. It is good that American strategists and our allies are coming to grips with the fact that this is a problem, but more must be done.

American shipyards need to be reinvigorated, producing more ships for commercial and military use; without the means by which to patrol the oceans and defend important SLOCs, policy will get nowhere. Freedom of navigation operations (FONOPs) need to be expanded in the Indo-Pacific and elsewhere to show that the world’s most populous country cannot unilaterally interdict open commerce or communications. This pace should ramp up, regardless of the hyperbolic Chinese reactions. America needs to go on offense diplomatically, working to undermine CCP influence near maritime choke points and offering a legitimate development alternative. Finally, the US must engage its allies in promoting the idea of the mare liberum for the 21st century and explaining to citizens and policymakers how critical the free sea is to global prosperity and security. Without buy-in from the public, it will be impossible to adequately counter the Chinese regime.

This century is seeing a return of the geopolitics of Great Powers, as well as the international issues that came with that dangerous, rivalrous world. The doctrines of mare liberum and mare clausum may date back to the 17th century, but are today relevant as ever. The battle between open oceans and shuttered seas is just beginning and China is surging ahead. The US and its partners should heed the lessons of the past and protect this crucial source of security and prosperity.