China's relations with the Socialist Republic of Vietnam began to deteriorate seriously in the mid-1970s. After Vietnam joined the Soviet-dominated Council for Mutual Economic Cooperation (Comecon) and signed the Treaty of Friendship and Cooperation with the Soviet Union in 1978, China branded Vietnam the "Cuba of the East" and called the treaty a military alliance. Incidents along the Sino-Vietnamese border increased in frequency and violence. In December 1978 Vietnam invaded Cambodia, quickly ousted the Pol Pot regime, and overran the country.