Although human rights concerns place limits on the depth of the U.S.-Cambodia relationship, a period of relative political stability in Cambodia that began in 2006, combined with U.S. regional security and strategic concerns, has led to a movement toward deeper bilateral ties. U.S. interests in the Kingdom of Cambodia include social, economic, and political development, trade and investment, regional security, civil society, and human rights. As China's economic and political influence has grown in Cambodia and the Lower Mekong Delta region, the Obama Administration has attempted to bolster U.S. ties with Cambodia and other countries in the region. A key challenge for U.S. policy toward Cambodia lies in combining and balancing efforts to engage the Kingdom on a range of fronts while promoting human rights and democracy. Some policy makers and experts contend that U.S. relations with Cambodia should be restricted until Prime Minister Hun Sen reverses a trend of deteriorating conditions for civil liberties and democratic institutions. According to some observers, Cambodia's close ties with China do not preclude improved relations with Washington, and Phnom Penh welcomes increased U.S. attention. The Obama Administration has taken tentative but meaningful steps toward strengthening U.S. ties with the Kingdom, particularly as Washington has sought to place greater foreign policy emphasis on East Asia. Hillary Clinton visited Phnom Penh in October 2010, the first visit by a U.S. Secretary of State in seven years, where she met with Prime Minister Hun Sen, King Norodom Sihamoni, opposition leader Mu Sochua, and others. During the trip, Secretary Clinton cautioned the Cambodians about becoming "too dependent" upon China. In June 2012, Cambodian Foreign Minister Hor Namong met with Clinton in Washington, DC, to discuss bilateral and regional issues. In July 2012, Secretary Clinton participated in the U.S.-Association of Southeast Asian Nations (ASEAN) Ministerial Meeting in Phnom Penh, where she spoke about U.S. support for ASEAN, maritime disputes in the South China Sea, and six strategic "pillars" of U.S. engagement in the region: regional security cooperation, economic integration and trade, engagement in the Lower Mekong region, transnational threats, democratic development, and war legacies. The former Secretary of State met with Hun Sen and participated in the U.S.-ASEAN Business Forum held at Siem Reap, near the famous temples of Angkor Wat. In November 2012, President Barack Obama traveled to Phnom Penh to attend the U.S.-ASEAN Leaders Meeting and the East Asia Summit (EAS). Obama was the first U.S. President to visit Cambodia. While in Phnom Penh, the President met briefly with Prime Minister Hun Sen—the usual protocol for a U.S. President on the sidelines of an EAS summit. During the meeting, Obama reportedly focused on human rights issues and urged the Cambodian leader to release political prisoners and allow opposition parties greater freedom. Human rights groups welcomed the call for improvements in Cambodia's human rights record, although some argued that the President should not have met Hun Sen at all. The U.S. government has devoted a small but sustained level of engagement with the Cambodian military, in part to maintain a degree of leverage in the Kingdom. U.S. military officials have expressed a desire for further cooperation with the Royal Cambodian Armed Forces (RCAF) as part of the Administration's policy of rebalancing toward Asia. U.S. military engagement in Cambodia includes naval port visits, military assistance, and joint exercises related to international peacekeeping, civic action and humanitarian activities, and maritime security. Washington began military contacts in roughly 2006 with a small International Military Education and Training (IMET) program worth $49,000 and a focus on counterterrorism cooperation. In the following years, two U.S. naval ships made port calls in Cambodia, the first in three decades, and U.S. military personnel launched training programs in counterterrorism and peacekeeping. Since 2010, U.S. and Cambodian military personnel have collaborated in bilateral and multilateral exercises. In 2012, the USS Blue Ridge visited Sihanoukville, Cambodia. Naval officers from both sides reportedly discussed joint exercises, coastal security, exploration and rescue, and other activities. In October 2012, U.S. and Cambodian naval forces participated in Cooperation Afloat Readiness and Training (CARAT) for the third year in a row, focusing on maritime security. In March 2013, the third annual Angkor Sentinel, a bilateral peacekeeping exercise held in Cambodia, took place in Kamong Speu. Cambodia owes the United States roughly $450 million (including $162 million in principal) for agricultural commodities provided by the U.S. Department of Agriculture to the Lon Nol government during the early 1970s. Cambodian officials have argued that many of the shipments never reached Cambodia, and asked the U.S. government to lower the interest rate on the debt and to return most of it (at least 70%) in the form of foreign aid. The U.S. government reportedly has already forgiven nearly $100 million, while U.S. officials have expressed a willingness to reschedule loan payments and return some payments as aid. However, U.S. officials have demanded that the Cambodian government first sign a bilateral debt agreement, acknowledging its obligations, and begin making payments before negotiations on debt terms begin. During their November 2012 meeting, President Obama remarked that his Administration would work to "find an acceptable solution for both sides." Cambodia is integrated in the global system through foreign aid ties, the international NGO community, regional organizations, and foreign trade and investment. The Kingdom is heavily dependent upon foreign aid from Japan, the United States, Australia, and Europe. Since 1996, the World Bank, other international financial institutions, and Development Assistance Committee (DAC) countries have attempted to coordinate aid and set economic and political reform guidelines for the Cambodian government through the Consultative Group for Cambodia and later the Cambodia Development Cooperation Forum. Cambodia is a member of the Association of Southeast Asian Nations and served as the organization's rotating chair for the first time in 2012. Cambodia has significant trade relations with neighbors Thailand and Vietnam, while its largest export market is the United States. In 2012, Cambodia served a one-year rotating term as chair of ASEAN. Many observers believe that Cambodia's deference to China, its principal economic patron, undermined ASEAN unity at meetings of ASEAN and the East Asia Summit. At the July 2012 ASEAN Ministerial, Phnom Penh's support for China's position on territorial disputes in the South China Sea aggravated tensions within the regional organization, resulting in the first failure in ASEAN's 45-year history to issue a joint communiqué. The tensions largely centered on the objections of Cambodia, as chair of the proceedings and allegedly at China's behest, to including a statement about the standoff between China and the Philippines at Scarborough Shoal. Beijing opposes ASEAN's involvement in what it perceives to be bilateral issues. Cambodia and Thailand, which once ruled parts Cambodia, have a history of conflict, although they share cultural traits and have strong economic ties. The two countries have experienced outbreaks of border tensions in recent years. In 2008, the long-simmering dispute over the sovereignty of land surrounding the 11 th century Khmer Preah Vihear temple, which lies in Cambodia, reignited after the United Nations (UNESCO) granted the site World Heritage status. The Thai government opposed the declaration, since it bolstered Cambodia's claims, although most access to the temple passes through Thailand. Border clashes between Thai and Cambodian troops have flared several times since 2008, resulting in over three dozen deaths, including Thai and Cambodian soldiers and civilians. Yingluck Shinawatra, Thailand's Prime Minister since 2011, has sought to repair ties with Cambodia. In April 2013, the International Court of Justice began hearings on the dispute. Relations between the Cambodian communists (Khmer Rouge) and the Vietnamese Communist Party (VCP) included mutual suspicion and periods of acrimony, culminating in the Vietnamese invasion and occupation of Cambodia in 1979-1989. The VCP provided support to some members of the current Cambodian leadership who had defected from the Khmer Rouge. Hun Sen, who served as Prime Minister (1986-1993) and Foreign Minister in the Vietnam-backed Peoples Republic of Kampuchea (see T extbox , below), has maintained close diplomatic, economic, and military relations with Hanoi. In April 2013, Cambodian and Vietnamese officials signed an agreement on defense cooperation, focusing on training, joint naval patrols, and other activities. Many Cambodians regard Vietnam with wariness stemming from the country's control over parts of the Kingdom prior to the French colonial period (1887-1953) and during the occupation of the 1980s. Some opposition leaders have criticized Hun Sen for cooperating with Hanoi in demarcating disputed border areas, asserting that he is ceding land to Vietnam. The People's Republic of China (PRC), once a major provider of military support to the Khmer Rouge, has become the leading foreign economic benefactor in the Kingdom of Cambodia. Some observers contend that Cambodia's foreign policies are heavily influenced by China, as evidenced by the Kingdom's support of China's positions during the 2012 ASEAN meetings. Other analysts believe that Hun Sen values and seeks relations with multiple foreign powers. Chinese economic interests are playing a growing role in Cambodia's development. The PRC is a major source of development assistance, largely in the form of concessional loans, Chinese-built infrastructure, and investment packages.