This year marks the 80th anniversary of the victory in the Chinese People's War of Resistance Against Japanese Aggression and the World Anti-Fascist War. Eighty years ago, in accordance with the Cairo Declaration and the Potsdam Proclamation, the Chinese government recovered the Nanhai Zhudao, restoring China’s sovereignty over them. This South China Sea order is an inseparable part of the post-war international order and enjoyed long-standing recognition from the international community.

Yet today, the situation in the South China Sea is turbulent. China’s sovereignty over these islands is being clouded by certain international narratives, and the post-World War II order in the South China Sea is facing erosion.

The Post-War Order in the South China Sea and Its International Legitimacy

International legal instruments such as the Cairo Declaration and the Potsdam Proclamation were key foundations of the post-war international order, and they also provided the legal basis for the post-war order in the South China Sea.

Between November and December 1946, Chinese government was tasked with organizing operations to recover the Xisha Qundao and Nansha Qundao, which had been occupied by Japan. The mission was successfully completed, with monuments reestablished, maps surveyed, resources inspected, and official ceremonies held on the islands, publicly declaring the restoration of China’s territorial sovereignty over the Xisha Qundao and Nansha Qundao.

In 1947, the publication of the Location Map of the Nanhai Zhudao and A Collection of Nanhai Zhudao Geographic Names and Documents further consolidated China’s claims. In 1948, the Chinese government incorporated the Location Map of the Nanhai Zhudao, featuring the 11-dashed-line marking, into the publicly issued Administrative division maps of the Republic of China, formally announcing to the international community the scope of China’s sovereignty and jurisdiction over the Nanhai Zhudao and adjacent waters. In this way, the post-war South China Sea order was established and broadly recognized internationally.

Historical records show that major powers, including the United States and the Soviet Union, widely recognized China’s post-war restoration of sovereignty over the Nanhai Zhudao. 

The United States not only supported Chinese officials in holding formal ceremonies on restoring the Xisha Qundao and Nansha Qundao, but for a long period also demonstrated recognition of China’s sovereignty through diplomatic inquiries, surveying requests, and notifications of navigation and overflight plans. U.S. publications, such as the 1961 Columbia-Lippincott Gazetteer of the World, the 1963 Worldmark Encyclopedia of the Nations, and the 1971 Encyclopedia of the Countries of the World, all affirmed China’s sovereignty over the South China Sea islands.

The Soviet Union’s 1952 Map of the Indochina and Indonesia rendered the Dongsha Qundao, Xisha Qundao, and Nansha Qundao in Chinese phonetic transliteration and marked them with “China” in parentheses. 

In the same year, Map 15, titled "Southeast Asia," from the 1952 edition of the Standard World Atlas—endorsed by then-Foreign Minister Okazaki Katsuo—clearly marked the Xisha Qundao, Nansha Qundao, Dongsha Qundao, and Zhongsha Qundao as Chinese territory. In 1972, the Joint Communiqué of the Government of the People’s Republic of China and the Government of Japan reaffirmed adherence to Article 8 of the Potsdam Proclamation, again confirming that the Nanhai Zhudao belong to China.

Other littoral states such as Malaysia and Indonesia did not protest China’s dashed-line claims. China’s sovereignty over these islands was also widely acknowledged by international organizations, including UNESCO.

Long-Term Undermining of the South China Sea Post-War Order

The erosion of the post-war order in the South China Sea has been a long-term process, shaped by complex factors involving international law, geopolitics, and energy interests.

The first wave of disruption came from U.S.-led “Ocean Enclosure” policies and the resulting great-power maritime hegemony. On September 28, 1945, President Truman issued the Policy of the United States With Respect to the Natural Resources of the Subsoil and Sea Bed of the Continental Shelf, asserting U.S. jurisdiction and control over the natural resources of the continental shelf adjacent to its coasts. The United States also advanced the concept of the Exclusive Economic Zone (EEZ).

As countries began making maritime claims, the drive to expand sovereignty and jurisdiction over the seas created a new round of “Ocean Enclosure.” Based on the four conventions adopted at the first United Nations Conference on the Law of the Sea in Geneva in 1958—the Convention on the Territorial Sea and Contiguous Zone, the Convention on the High Seas, the Convention on Fishing and Conservation of Living Resources of the High Seas, and the Convention on the Continental Shelf—this era reflected and protected the interests of traditional maritime powers, shaping the contemporary international maritime order.

The discovery of oil and gas resources in the South China Sea in the late 1960s and early 1970s, coupled with ongoing UNCLOS negotiations, prompted littoral states like the Philippines to invoke continental shelf and territorial sea regimes to assert sovereignty claims, marking the origin of the modern South China Sea disputes. This constituted a serious and substantive disruption of the post-war South China Sea order.

Claimant states like the Philippines have sought to over-interpret provisions of UNCLOS, asserting sovereignty over some of China’s Nansha Qundao based on maritime jurisdiction, or using illegally occupied features to further claim territorial seas, contiguous zones, EEZs, and continental shelves. For example, on June 11, 1978, the Philippines unilaterally declared 33 islands, reefs, and shoals in the Nansha Qundao—covering 64,976 square nautical miles—as the so called “Kalayaan Island Group,” claiming them as part of Philippine territory and administering them. From the 1970s to 1999, the Philippines, Vietnam, and other claimants continuously expanded illegal occupations.

Since the end of the Cold War, particularly after 2009, the South China Sea disputes have evolved beyond territorial and maritime claims, becoming a regional security hotspot and a front of great-power strategic competition. In this context, the post-war order in the South China Sea has faced unprecedented challenges.

First, extra-regional powers such as the United States and Japan have shifted their South China Sea positions. For example, U.S. policy evolved from engagement under the Clinton administration to strategic intervention under the Trump administration, emphasizing “freedom of navigation” and “freedom of overflight” and supporting the claims of other littoral states. Consequently, the South China Sea has become a key arena of great-power competition, especially militarily and in maritime order.

Second, the 2013 Philippine-initiated “South China Sea arbitration” and the 2016 unlawful “ruling” have been leveraged by the U.S. to challenge China’s claims and further undermine the post-war order, influencing other claimants to justify encroachments or bolster their illegal claims.

The dashed-line claim and official maps are concrete manifestations of the post-war South China Sea order, predating UNCLOS by half a century and the Geneva conventions by over a decade. Yet, due to factors including international law, geopolitics, and energy interests, this order has been long undermined, and the South China Sea has become a critical pivot linking global changes with regional dynamics.

Currently, China and ASEAN are effectively implementing the Declaration on the Conduct of Parties in the South China Sea (DOC) and negotiating the Code of Conduct in the South China Sea (COC), a shared effort to build a cooperative and secure maritime order. It is important to note, however, that China’s sovereignty over the Nanhai Zhudao, its maritime rights, and the post-war order established after World War II remain the essential premise and foundation for any discussion on resolving disputes in the South China Sea—they must be fully respected and maintained.

(Author: Ge Hongliang, Deputy Dean of the College of ASEAN Studies at Guangxi Minzu University and Special Invited Researcher of the CMG Expert Committee on South China Sea Studies)