Sihanouk's method of alternately criticising his opponents in various public forums, and then of offering them posts within the Sangkum in a demand that they positively contribute to Cambodian society, had the dual effect of stifling dissent and of integrating much of the opposition into his regime. Sihanouk attempted to construct an image of Cambodia as a "Southeast Asian
Camelot", an oasis of peace and social order amidst the conflict affecting the rest of the region. Internationally, an official policy of
neutrality was adopted. During the period of Sihanouk's rule, the Sangkum managed to absorb many of the rightist and centrist elements of Cambodian politics, as well as pro-Sihanouk elements of the left and moderate communists: only the more hardline secret elements of the
Communist Party of Kampuchea avoided collaborating with Sihanouk's regime. Several prominent communists, such as
Hu Nim and
Khieu Samphan, accepted posts with the Sangkum in an attempt to work with the system. In the early 1960s, Samphan – later to become the head of state under the
Khmer Rouge – was called on by Sihanouk to implement a series of economic reforms based on plans outlined in Samphan's PhD thesis. While the Democratic Party, the representatives of moderate, progressive
republican politics in the Cambodian political milieu, were effectively incorporated into the Sangkum in 1957, many republican moderates simply avoided politics altogether until the period immediately after 1970. The only notable element to remain outside the Sangkum, other than the hardline communists, was the right-wing, anti-monarchist nationalist
Son Ngoc Thanh, whose
Khmer Serei irregulars maintained armed resistance with funding from
Thailand. Sihanouk was to label his opponents on the right as the "Khmer Bleu" to distinguish them from his opponents on the left. However, it seems that during the late 1950s and early 1960s there was relatively little violent repression of opposition to the Sangkum (although there was repeated political intimidation of the leftist
Pracheachon party, who were accused of being pro-Vietnam) and the country as a whole experienced a period of comparative stability. The one exception was again the Khmer Serei, who were dealt with harshly:
Preap In, a Khmer Serei activist who attempted to negotiate with Sihanouk in 1963, was arrested and his subsequent execution shown in cinemas across the country. The same treatment was given to another group of alleged Khmer Serei leaders, Chau Bory (previously implicated in the
Bangkok Plot), Chau Mathura, and Sau Ngoy, in 1967. ==End of the Sangkum era==