Heng Samrin was elected the president in the general election in May 1981. But their government was isolated since the international society regarded the Pol Pot government as a legitimate government in Cambodia. The countries under the Soviet Union's influence supported the Heng Samrin government. The United States, China, Japan, the western Europe countries and ASEAN didn't recognize the new government and insisted that Vietnam should withdraw the troops. They intended to block the Soviet Union's intention to expand their influence to Indochina peninsular by keeping Vietnam out of Cambodia.

The Pol Pot government, expelled by Vietnam, appointed Khieu Samphan as the prime minister and formed the Patriotic and Democratic Front of the Great National Union of Kampuchea (GRUNK), of which Khieu Samphan. They stayed at the frontier between Thailand and Cambodia and launched guerilla warfare.