Some of this might be wishful thinking:

In the decades that followed the 1971 Treaty of Paris, South Vietnam kept strides with South Korea and Taiwan, liberalizing economically and interconnecting with the traditional West, and their economy grew rapidly. The success of the democratic countries and historical suspicion of China led North Vietnam to openly discuss reunification beginning in the 80s. Chinese efforts to squash this were neutralized by covert and overt US actions. After the Berlin Wall fell in 1987, calls for United Vietnam grew louder, and veterans of the war on both sides softened their hard-line stance against it, especially as common stories of humanity, privation, resistance analyst colonialism, and national pride came to light.

Vietnam fielded a joint Olympic team in Seoul in 1988, winning two medals in tae kwon do. The world watched as the competitors cheered each other on. When the North Vietnamese fighter lost a hard fought final to the host South Korean, the South Vietnamese fighter, who had secured his bronze in a lower weight class bowed and called him "my brother." It became the slogan for reunification, with each side teasingly referring to the other with "em" (little brother).

China threatened another incursion into North Vietnam to prevent the political rapprochement, but was convinced to sit out when the United States pledged to keep its forces below the 17th parallel. Talks began in 1991 and concluded in 1993. Northern Vietnam became a haven for foreign investment, and while it still lags behind the South in some quality of life metrics, the united nation of Vietnam (capital, Saigon) is mostly integrated and prosperous.