Cambodia’s hegemonic party system that emerged after the violent removal of First Prime Minister Norodom Ranariddh early in July 1997 has now given way to a one-party state, which still remains prone to tension and instability. The party system has become less factionalised and can be characterised as moving from high to medium factionalism. This development resulted from the growing domination of the Cambodian People’s Party (CPP) and the weakening of the opposition parties, such as National United Front for an Independent, Netural, Peaceful and Cooperative Cambodia, which splintered and become almost irrelevant in Cambodian politics. The Cambodian National Rescue Party (CNRP) emerged as the main opposition party after the 2013 election but was then banned from competing in the 2018 election. Although the CNRP remains united by its anti-CPP position, it is still fractured along political lines between two former opposition parties – the Sam Rainsy Party and the Human Rights Party. Historical institutionalism sheds some new light on the variation of political developments among political parties and within them, but does not supplant the fact that party leaders are rational to the extent that they select strategies in pursuit of their interests defined as power or security under specific institutional constraints or the lack thereof.