When and why did the “Vietnam syndrome” arise?

Vietnamese syndrome was called severe mental illness in Vietnam war veterans, associated with a large number of injuries and types of deaths, as well as an awareness of the severity of what the soldier himself could bear in another country. From this, the veterans who returned to the United States often could not integrate into the rhythm of life, often sinking to the bottom of society. A similar syndrome arose en masse by the end of the 1960s, when Americans began to return home after service. It manifested itself especially strongly in the 1970-80s.