Under the 1963 constitution, Massamba-Débat was elected President for a five-year term. During Massamba-Débat's term in office the regime adopted "scientific socialism" as the country's constitutional ideology. In 1965, Congo established relations with the Soviet Union, the People's Republic of China, North Korea and North Vietnam. Massamba-Débat's regime also invited several hundred Cuban army troops into the country to train his party's militia units and these troops helped his government survive a coup in 1966 led by paratroopers loyal to future President Marien Ngouabi. Nevertheless, Massamba-Débat was unable to reconcile various institutional, tribal and ideological factions within the country and his regime ended abruptly with a bloodless coup d'état in September 1968.