In late January last year, China donated 100 tanks to Cambodia. And the militaries of the two countries just celebrated their 60th anniversary of Sino-Cambodia diplomatic relations by concluding their joint annual Golden Dragon military exercises on Thursday.
While Cambodia-China military to military relations are intensifying, Cambodia's military relations with Western countries, particularly the United States and Australia, are on the decline in recent years.
In January last year, the Royal Cambodian Armed Forces (RCAF) unilaterally cancelled Angkor Sentinel, an annual joint military exercise between Cambodian and US militaries without giving an explanation. A few months later, the US Navy Mobile Construction Battalion, best known as "Seabees", was requested to leave Cambodia by the Cambodian government, leaving many humanitarian projects unfinished across a number of provinces.
Also, the Cambodian government called off "Dawn Kouprey", a cornerstone joint military exercise on counter-terrorism between Cambodia and Australia in March 2017.
Describing the move by the RCAF to distance itself from the West as poor professionalism, Carl Thayer, an emeritus professor at the Australian Defence Force Academy, believed that domestic politics rather than geopolitics was a motive. Paul Chamber, a lecturer at Naresuan University in Thailand, argued that the growing influence of China was a reason.
Although neither of these observers is wrong, I argue that the twilight of the US-Cambodia military relations resulted from not only Cambodia's domestic politics and the growing influence of China in Cambodia, but the changes in the US Asia strategy after the arrival of the Trump administration in 2016.
Firstly, waxing and waning US Asia strategies weakened America's credibility in the eyes of allies and liked-minded friends and created a power vacuum for the opponents of the United States to fill and exploit.
Just a day before the then US Secretary of State Rex Tillerson began his first visit to Asia on March 14 last year, Susan Thornton, acting assistant Secretary of State for the Bureau of East Asian and Pacific Affairs, confirmed that "the pivot to Asia is over".
The Trump administration entered the White House only to replace Barack Obama's "rebalance to Asia" with "America First", an inward-oriented policy to please Mr Trump's electoral base. While it is clear that the Asia-Pacific region will be the primary theatre of US foreign policy in the 21st century, Mr Trump's "America First" has become an unclear strategy that generates not only diplomatic uncertainty among US security allies, strategic partners and like-minded friends in Asia, but also gives China and authoritarian states more room to take advantage of waning US-Asia strategies.
Cambodia, in particular, is seeking greater relations with regional superpowers, such as China and Russia to fill the US vacuum and foreign policy vacillation.
Secondly, Mr Trump's "America First" policy seems to reinvigorate the late Dean Acheson's concept of "the defence perimeter", which defined the US military and security interests in the Asia-Pacific as maritime rather than continental.
Further, Kurt Campbell, a former Assistant Secretary of State for East Asia and Pacific and a key architect of the Obama rebalance to Asia, argues that Asia was rarely the primary theatre, but always the secondary theatre or sometimes the "forgotten theatre" of the US foreign policy. This relegation is despite Asia being home to the fastest growing economies, massive military modernisation including nuclear proliferation and maritime security flashpoints. Mr Campbell's observations are set out in his most recent book The Pivot: The Future of American Statecraft in Asia.
However, in their newly-published book, Avoiding the Trap: U.S. Strategy and Policy for Competing in the Asia-Pacific Beyond the Rebalance, David Lai, John F Troxell and Frederick J Gellert, Asian security experts from the US Army War College, argue that Mr Trump's America First indeed intensified deeper US engagement with the Asia-Pacific. This interpretation refers to the visit of Japan's Prime Minister Shinzo Abe to the US as the first state visit hosted by President Trump and the first visits to Asia by senior officials from State Department and Defence Department.
These arguments, nonetheless, are weak following Mr Trump's initial reluctance to attend, and then finally changed his mind, the Asean-hosted East Asia Summit in the Philippines in late 2017. It demonstrates that his administration is not interested in Asean, the largest regional institution in the Asia-Pacific, which Victor Cha, a former director of the National Security Council during the Bush Administration, called a "talk shop".
Although the Trump administration reinvigorated US diplomacy with the Thai junta and engaged with Vietnam, the relations are bilateral, as Thailand is a US security ally, while Vietnam is a US strategic partner.
It is true that Cambodia is small and its geopolitical roles might not feature in the US Asia strategy. Yet Cambodia's roles as a spoiler in the multilateral framework should not be underestimated.
The case was clear when Cambodia was chairing Asean in 2012. It declined to include the Scarborough Shoal incident in the regional grouping's joint statement following the naval tensions between China and the Philippines. It was the first time in Asean history since 1967 that the summit concluded with no joint communiqué. Even if Cambodia denied any interference from China, the real beneficiary of this stumbling block was China, which has always objected to internationalising the disputes in the South China Sea.
While the US has devoted extensive resources and efforts to shoring up maritime security in Southeast Asia through the Southeast Asia Maritime Law Enforcement Initiative and the Southeast Asia Maritime Security Initiative, Cambodia's chairmanship of Asean and its refusal to offend China was a bitter experience for America. The cost in terms of the US military engagement with Cambodia is relatively low. However, the price the US pays for regional security and maritime order following Cambodia's diplomatic about-turn is high.
As the Trump administration has repeatedly referred to US supremacy in the "Indo-Pacific", actually maintaining international order in the region will become critically challenging without the cooperation of small states in Asean.
Thirdly, the ongoing turbulent domestic politics in the US has diluted American unity towards external threats. As Mr Campbell pointed out, "domestic deadlock has always had repercussion for US standing in Asia."
The government shutdown over the issues of debt ceiling and immigration, for example, signals the growing polarisation of American politics, drawing the attention and energies of American politicians elsewhere, thus leaving external challenges and promotion of universal values, such as democracy, liberty and human rights, on the sideline.
The decline of US-Cambodia relations resulted from not only the recent curb on Cambodian domestic politics and the growing influence of China in Cambodia, but also changes in the US Asia strategy after Mr Trump arrived at the White House.
The growing trends of domestic challenges and polarisation of American politics have ruined the national unity of American policymakers. Unsurprisingly, Cambodia's Prime Minister Hun Sen took this opportunity to distance himself from the West in order to show his "vassal loyalty" to China in exchange for unconditional economic and political support against the West, particularly the US.
Cutting aids and downgrading military to military relations with Cambodia amid the surge of China's influence in Asia is not the US strategy of choice, given the US long-standing commitment to rule-based order and universal values of freedom, democracy and human rights.
Sek Sophal is a researcher at the Democracy Promotion Centre, the Ritsumeikan Center for Asia Pacific Studies, Beppu, Japan.