On what date did North and South Vietnam merge to form the Socialist Republic of Vietnam?

On 2 July 1976, North and South Vietnam were merged to form the Socialist Republic of Vietnam. The war left Vietnam devastated, with the total death toll standing at between 966,000 and 3.8 million. In the aftermath of the war, under Lê Duẩn's administration, there were no mass executions of South Vietnamese who had collaborated with the US and the defunct South Vietnamese government, confounding Western fears. However, up to 300,000 South Vietnamese were sent to re-education camps, where many endured torture, starvation, and disease while being forced to perform hard labour. The government embarked on a mass campaign of collectivisation of farms and factories.

In 1978, as a response towards the Khmer Rouge who had been invading and massacring Vietnamese residents in the border villages in the districts of An Giang and Kiên Giang, the Vietnamese military invaded Cambodia and removed them from power after overtaking Phnom Penh. The intervention was a success, resulting in the establishment of a new pro-Vietnam socialist government, the People's Republic of Kampuchea which ruled until 1989. This action, however, worsened relations with China, who had been supporting the Khmer Rouge and they later launched a brief incursion into northern Vietnam in 1979 and caused Vietnam to rely even more heavily on Soviet economic and military aid, while mistrust towards the Chinese government began to escalate.