The Japan Forum on International Relations

May 09,2024

China–Cambodia “Diamond Hexagon” Cooperation Framework and Japan

■ China is fortifying its military influence in the South China Sea and CLM

The three least economically developed countries of ASEAN, Cambodia, Laos, and Myanmar (CLM), are attracting attention in Japan in the context of “China plus one” and “Thailand plus one”. One of those countries, Cambodia, has a favorable image of Japan. Nevertheless , having relied heavily on Chinese aid, Cambodia has become increasingly subservient to China, making its pro-China stance clearer than most Southeast Asian countries. About 90% of the investment projects approved by the Cambodian Development Council in 2022 were linked to China. According to the Cambodian Ministry of Economy and Finance (MEF), more than 40% of Cambodia’s $10 billion in external debt is owed to China[1], leaving Cambodia caught in a Chinese “debt trap”[2]. On May 6, 2024, China and Cambodia held “Golden Dragon 2024,” a joint China-Cambodia military exercise in Cambodia from mid to late May to enhance the level of strategic cooperation between the two militaries, according to an announcement by the Chinese Ministry of National Defense.

Even with Cambodia’s advocacy of a policy of neutrality and diplomacy in all directions, concerns have arisen about Cambodia’s excessive dependence on China. It has been reported worldwide that Cambodia has signed a secret agreement with China allowing exclusive use of part of the Liam Naval Base. Also, reportedly, China has begun to deploy its warships on a semi-permanent basis as a means of strengthening its military influence in the South China Sea and the CLM[3]. China’s interest in Cambodia extends beyond Cambodia’s geopolitical location; it may also aim to prevent ASEAN from unifying against China’s actions in the South China Sea using the CLM countries as “pawns.”

This commentary discusses Cambodia’s deepening “ironclad friendship” with China in the framework of “Diamond Hexagon” cooperation (“钻石六边” 合作架构) and the Chinese presence at the Cambodian port of Liam and the airport at Dara Sakor, 65 kilometers (km) northwest of Liam. Moreover, this commentary will examine Japan’s diplomacy with Cambodia in light of the perceived implications these developments have for the South China Sea and for Japan’s security environment.

■ Proposal for a “Japan Special Zone” by Cambodia, a country that is increasingly “leaning toward China”

Cambodia has been expanding its cooperation with China through the “One Belt, One Road” initiative, which serves as a platform for China’s expanding influence, and also through the “Diamond Hexagon” cooperation framework between the two countries. Since the mid-2000s, Chinese aid to Cambodia has expanded rapidly. In 2010, China replaced Japan as Cambodia’s largest bilateral donor. In fact, China accounts for a large share of Cambodia’s aid and foreign direct investment (FDI) . The Cambodian administration is increasingly dependent on China[4].

However, many Chinese real estate companies have pulled out of Sihanoukville in southern Cambodia, leaving behind hundreds of unfinished and unused buildings and plunging the country into a “debt trap.” Under these circumstances, Cambodia has proposed to Japan, the U.K., India, Malaysia, Thailand, and other countries a special economic zone concept based on bilateral cooperation, intended to promote FDI in Cambodia.

Cambodia’s prime minister was replaced by hereditary succession in August 2023 for the first time in 38 years, with Hun Manet succeeding Hun Sen. On December 18, 2023, during Prime Minister Hun Manet’s visit to Japan to attend the Japan-ASEAN 50th Anniversary Commemorative Summit, Japan’s Prime Minister Fumio Kishida met with him and expressed a desire to strengthen relations in the security field through personnel exchanges, port calls, and other forms of unit-to-unit exchanges. The two prime ministers agreed to establish a defense vice-ministerial meeting in addition to the foreign vice-ministerial meeting held for the first time in November of the same year, to advance cooperation in the security field. Additionally proposed was the establishment of a special economic zone specifically for Japanese companies.

Japan needs to develop its policy toward Cambodia by considering this special economic zone proposal not only from the perspective of bilateral business relations between Cambodia and Japan but also from the geopolitical context of the Indo-Pacific region.

■ The “Diamond Hexagon” Cooperation Framework between China and Cambodia

In 2023, which marked the 65th anniversary of the establishment of diplomatic relations between China and Cambodia, the two countries celebrated the “China–Cambodia Friendship Year.” During this period, then-Prime Minister of Cambodia, Hun Sen, made an official visit to China during February 9–11 (accompanied by his eldest and third sons). Both prime ministers reaffirmed the close ties between their nations and issued a joint statement pledging to advance the “Comprehensive Strategic Cooperative Partnership” between Cambodia and China and to collaborate in building a community of shared destiny. They agreed to enhance bilateral cooperation through the framework of “One Position, Six Cooperation Areas, and Two Corridors.[5]

“One Position” refers to the “ironclad friendship” described in the joint statement[6], which declares that ” irrespective of how the international situation changes, China and Cambodia will deepen their unwavering friendship, engage in mutually beneficial practical cooperation, and promote the building of a community with a shared future.” This expression represents the stance that both countries will adopt in their efforts to construct a “China-Cambodia Community of Shared Destiny” in the “New Era.[7]

“Six Areas of Cooperation” refers to collaboration in the fields of politics, manufacturing, agriculture, energy, security, and cultural exchanges under the framework called the “Diamond Hexagon Cooperation.” The “hexagon” signifies a six-sided shape, representing these six areas. The “diamond” symbolizes a clear message from Hun Sen to Xi Jinping, conveying that “the Cambodian people are always firmly connected with the Chinese people.”

“Two Corridors” refers to the “Industrial Development Corridor” developed around Sihanoukville Province and the “Fish and Rice Corridor” in the Tonle Sap Lake region. Xi Jinping assured Hun Sen that China would encourage more Chinese companies to invest in Cambodia to build the “Industrial Development Corridor” and to promote the Sihanoukville Special Economic Zone (SSEZ). The “Fish and Rice Corridor” involves the creation of a modern agricultural system for fish and rice around the lake, a joint initiative agreed upon by both countries to foster agricultural cooperation.

Iron is highly durable against impact ; and diamond has a high hardness. The “ironclad friendship” designated as “One Position” and the “Diamond Hexagon” designated as the “Six Areas of Cooperation” form the foundation for building the “China-Cambodia Community of Shared Destiny” in the “New Era.” (However, diamonds are also vulnerable to forces exerted from certain directions, can crack upon impact, and can lose their luster because of oil.)

■ Deep-draft pier capable of accommodating aircraft carriers and Chinese ships

In the years since the U.S.-funded facilities at Liam Naval Base in southwestern Cambodia were demolished and replaced by Chinese-funded projects, the U.S. State Department and Pentagon have frequently issued warnings that they have “serious concerns” and that they are closely watching China’s plans for exclusive control of a portion of Liam Naval Base. If a facility for both military and civilian use were built at Liam Port, located near Sihanoukville Airport, and were turned into a Chinese base, the Chinese Navy would have a geopolitical foothold in the South China Sea, the Malacca Strait, the Lombok Strait, Thailand, and Vietnam.

At the Port of Liam, which is reportedly about to be “renovated,” a new facility with a pier reported to have “a draft deep sufficient to accommodate the Chinese aircraft carrier Fujian[8]” is already under construction. The first foreign vessels to access it in early December 2023 involved at least two vessels of the Chinese People’s Liberation Army (escort corvettes “Wenshan” and “Bazhong”). The Russian Navy’s submarine destroyer “Admiral Panteleyev”, which had docked in Cambodia on November 27, docked at the port of Sihanoukville, approximately 20 km away from there. The Japanese Maritime Self-Defense Force naval destroyer “Suzunami” and training ship “Shimakaze”, which docked on February 22, 2024, also docked at the port of Sihanoukville.

Cambodian Defense Minister TEA Seiha, along with her father and predecessor TEA Banh[9] posted on social media that they “visited the base, which is currently under construction with Beijing’s assistance,” and “inspected the infrastructure construction that is actively underway according to the plan.” “Chinese vessels provided onboard and in port training to Cambodian naval personnel,” and “will bring the navy’s capabilities to a higher level.[10]” These arrangements and activities demonstrates the People’s Liberation Army Navy’s deep military involvement in Cambodia. The military and political implications of the port of Liam will be clarified by satellite imagery reports from the United States and other Western countries that will be monitoring the frequency of access by Chinese naval vessels and their port calls against other navies and naval forces over the next several years.

In addition, the U.S., Japan, and the rest of the world should devote to how the Dara Sakor Airport, which was built in Koh Kong Province as part of the “One Belt, One Road” project, will be used. It is noteworthy that the airport was scheduled to become operational in early 2021. However, because of the COVID pandemic and other factors, it was postponed repeatedly. As of May 9, 2024, the date of this report’s drafting, the airport had not yet opened.

The Dara Sakor development project dates back to 2008 when UDG, based in Tianjin, China, signed a 99-year lease agreement with the Cambodian government to build an international airport, deep-sea port, industrial park, and luxury resort facilities in a special economic zone. The Dara Sakor project by UDG is expected to construct a multipurpose facility complex that uses approximately 20% of the coastal area of Cambodia, but the “development” is skewed toward the airport and the deepwater port. Reportedly, plans also exist for a 3,300-meter (m) runway at Dara Sakor Airport, as well as additional runways of 3,800 meters and 3,200 meters. The U.S. Department of Defense has repeatedly expressed concern over the past several years that the Dara Sakor Airport can potentially serve as a dual-use military and civilian airfield for China. A runway of that length would allow for takeoffs and landings by H6 bombers and Y-20 large transport aircraft.

Comparing the expected volume of people and goods traffic at Dara Sakor with that of Japanese airports raises doubts about the intended use of Dara Sakor Airport. Narita Airport in Japan has a 4,000-meter Runway A and a 2,500-meter Runway B. The amplification plan, to be completed by March 31, 2029, with the aim of increasing annual arrival and departure capacity to 500,000 flights, calls for the extension of Runway B from 2,500m to 3,500m, along with the construction of a new 3,500m long Runway C, and a total of 7,471m of new and improved taxiways. Using the figures for Narita Airport as a reference, can the length and function of the runway be considered reasonable, given the scale of Cambodia’s economy and tourism industry, and given the arrival and departure capacity of the Dara Sakor Airport?

For security of the Indo-Pacific, Japan’s government and public opinion should also be vigilant about China’s intended use of the important geopolitical chokepoint from the port of Liam to Dara Sakor.

■ Questioning Japan’s Development Cooperation with “China-oriented Cambodia”

For many years, Japanese diplomacy has been devoted to promotion of peace and prosperity in the international community. Japan has worked to boost the development of developing countries through official development assistance (ODA) and other forms of development cooperation. In this context, Japan’s “Outline of Development Cooperation” has been designed to contribute actively to ensuring peace, stability, and prosperity in the international community, while adhering to the principle of avoiding the use of development cooperation for military purposes or for promoting international conflict.

Cambodia has deepened its relations with China in the security sphere. In the event of conflict in the South China Sea or Taiwan, significant risk exists that Liam and Dara Sakor and other key infrastructure might be used by the Chinese military. Japan’s development assistance to Cambodia is not involved directly in military applications at this time. However, careful consideration of the relations forming along with development projects by China will be increasingly necessary when formulating development assistance from Japan to Cambodia.

The percentage of the elderly population among Japan’s total population reached a record high of 29.1% in 2023. Moreover, the percentage of the population aged 75 and older reached a record high of 16.1%. Japan’s Japan’s financial circumstances have become increasingly strained. Especially given that context, foreign aid must contribute more than ever to Japan’s national interests, particularly peace and security in the Indo-Pacific region. Japan’s diplomacy with Cambodia in the Indo-Pacific at a time of intensifying competition for spheres of influence between the U.S., China, and Russia should be conducted with specific scrutiny of the development of the “diamond hexagon” relationship between China and Cambodia.

(Originally published on May 9, 2024)

[1] “Chinese warships leave Cambodia’s Ream naval base,” Radio Free Asia, January 16, 2024 [ Last accessed May 8, 2024. All URLs mentioned below were last accessed on May 8, 2024.
[2] The term “debt trap” refers to a situation in which a country that has received international aid and is struggling to repay its debts is pressured by the creditor country in terms of policies or diplomacy, leading to scenarios in which the creditor country confiscates the infrastructure built with the loans or demands military cooperation.
[3] Providing military bases to foreign countries violates Article 53 of the Cambodian Constitution. Therefore, the Cambodian government completely denies any “stationing of Chinese troops” or “leasing to the Chinese military.”
[4] For instance, according to the Ministry of Foreign Affairs’ “Basic Data on the Kingdom of Cambodia,” the main aid donors and their support amounts (estimated values for 2020, in million US dollars) were China (421.6), Japan (336.5), ADB (283.1), World Bank (140.8), EU (90.3), South Korea (58.0), and the United States (43.9) []. According to the IMF’s Direction of Trade Statistics for 2021, Cambodia’s trade included the following: China – exports $1.51 billion US dollars (8.6% of total exports), imports $9.68 billion (33.6% of total imports); Japan–exports $1.09 billion (6.2% of total exports), imports $0.64 billion (2.2% of total imports); United States –exports $7.49 billion (42.7% of total exports), imports$0.34 billion (1.2% of total imports); ASEAN–exports $1.18 billion (6.7% of total exports), imports $12.92 billion (44.8% of total imports). The United States has a notable presence in exports, whereas China dominates imports.
[5] 中华人民共和国外交部「中华人民共和国和柬埔寨王国关于构建新时代中柬命运共同体的联合声明(全文)」February 11, 2023 [].
[6] Op. cit.
[7] In an extremely long speech at the 19th National Congress of the Communist Party of China (the so-called “Party Congress,” held once every five years) in October 2017. Xi Jinping stated, “The time has come for China to take the center stage in the world,” and “This means that China has become a great power in the world,” signifying an era where China is positioned at the center of the international order. It does not merely mean a new era.
[8] “Fujian” is China’s third most advanced aircraft carrier, launched in Shanghai in June 2022. It was previously reported that “Jiangsu” was a strong candidate, but in an expanded meeting of the Central Military Commission held in early June of the same year, it was reported that Xi Jinping, Chairman of the Central Military Commission, proposed the name “Fujian.”
[9] Despite having passed on his position to his son, he still maintains a strong influence in military affairs.
[10] “Chinese warships dock at Cambodia’s Ream naval base for ‘training’,” December 5, 2023, Radio Free Asia, [].

This work was supported by JSPS KAKENHI Grant Number JP24K04762