1977, and the execution of Colonel Atnafu Abate in November 1977, Mengistu gained undisputed leadership of the Derg. In 1987, he formally dissolved the Derg and established the country as the People's Democratic Republic of Ethiopia (PDRE) under a new constitution. Many of the Derg members remained in key government posts and also served as the members of the Central Committee and the Politburo of the Workers' Party of Ethiopia (WPE). This became Ethiopia's civilian version of the Eastern bloc communist parties. Mengistu became Secretary-General of the WPE and President of the PDRE while remaining the Commander in Chief of the Armed Forces. Ethiopian Civil War Opposition to the reign of the Derg was the main cause of the Ethiopian Civil War. This conflict began as extralegal violence between 1975 and 1977, known as the Red Terror, when the Derg struggled for authority, first with various opposition groups within the country, then with a variety of groups jockeying for the role of vanguard party. Though human rights violations were committed by all sides, the great majority of abuses against civilians as well as actions leading to devastating famine were committed by the government. The Ethiopian Orthodox Church, which represents the Christian state church of Ethiopia for centuries, was disestablished in 1974. The Derg declared a policy of state atheism, a tenet of Marxism-Leninist ideology; this was opposed by the vast majority of the Ethiopian population. Once the Derg had gained victory over these groups and successfully fought off an invasion from Somalia in 1977, it engaged in a brutal war against armed opponents within the country. These grouped ranged from the conservative and pro-monarchy Ethiopian Democratic Union to the far-leftist Ethiopian People's Revolutionary Party. Other groups included Eritrean People's Liberation Front (EPLF) guerrillas fighting for Eritrean independence, rebels based in Tigray (which included the nascent Tigray People's Liberation Front) and other groups. Under the Derg, Ethiopia became the Soviet bloc's closest ally in Africa and became one of the best-armed nation of the region as a result of massive military aid, chiefly from the Soviet Union, East Germany, Cuba and North Korea. On 4 March 1975, the Derg announced a program of land reform, according to its main slogan of "Land to the Tiller", which was unequivocally radical, even in Soviet and Chinese terms. It nationalized all rural land, abolished tenancy and put peasants in charge of enforcing the whole