On September 20, 1977, the Socialist Republic of Vietnam was admitted to the United Nations as its 149th member, two and a half years after the fall of Saigon ended the war. The application had been blocked by the United States in 1976, on the argument that Vietnam had not accounted for the Americans missing in action, and Washington dropped the veto in 1977 after the Vietnamese handed over the remains of 12 airmen.
The war had ended on April 30, 1975, when North Vietnamese tanks entered the Presidential Palace in Saigon, and the country was formally reunified in July 1976 under the name it had used in the north since 1945. Before that, two states had claimed the whole country and neither was in the UN: the Republic of Vietnam in the south had applied in 1957 and 1958 and been blocked by the Soviet Union, and the Democratic Republic of Vietnam in the north had applied and been blocked by the United States.
Vietnam wanted money and recognition. The country had taken enormous damage: an estimated two to three million Vietnamese dead, about half the country's rubber plantations and a large part of its bridges and rail destroyed, and millions of tonnes of ordnance and herbicides dropped on it. The government had also just nationalised the economy in the south, and the harvests of 1976 and 1977 were bad.
It got nothing. The United States kept a trade embargo, blocked loans from the World Bank and the IMF, and opposed reconstruction aid, and it was joined by China, which had been Vietnam's largest donor and had cut off all assistance in 1975. Then the foreign policy collapsed around Vietnam: it signed a treaty with the Soviet Union in November 1978, invaded Cambodia in December and installed a government there, and in February 1979 China sent about 200,000 troops across the northern border in a punitive invasion that lasted a month.
Vietnam stayed in Cambodia for ten years. It withdrew in 1989. It normalised relations with China in 1991 and with the United States in 1995, and joined the World Trade Organisation in 2007. It has been a non-permanent member of the Security Council twice. The population has roughly doubled since 1975, and about 40 per cent of it was born after the war ended.