In 1975–1976, there were several powerful zonal Khmer Rouge leaders who maintained their own armies and had different party backgrounds than the members of the Pol Pot clique, particularly So Phim and Nhim Ros, both of whom were vice presidents of the state presidium and members of the Politburo and Central Committee respectively. A possible military coup attempt was made in May 1976, and its leader was a senior Eastern Zone cadre named Chan Chakrey, who had been appointed deputy secretary of the army's General Staff. A reorganisation which occurred in September 1976, during which Pol Pot was demoted in the state presidium and was later presented as an attempted pro-Vietnamese coup by the Party Center. Over the next two years, So Phim, Nhim Ros, Vorn Vet and many other figures who had been associated with the pre-1960 party were arrested and executed. Phim's execution was followed by that of the majority of the cadres and much of the population of the Eastern Zone that he had controlled. The Party Centre, lacking much in the way of their own military resources, accomplished their seizure of power by forming an alliance with Southwestern Zone leader Ta Mok and Pok, head of the North Zone's troops. Both men were of a purely peasant background and were therefore natural allies of the strongly peasant ideology of the Pol Pot faction.