The Montagnards are made up of dozens of tribes, each with their own dialect and customs, such as the Rhade, Jarai, and others. Although the majority lived in Vietnam, they are not closely related to ethnic Vietnamese, and were treated poorly and forced into the central highlands, away from the more heavily-populated and hospitable coastal areas.
It is notable that during the Vietnam War, over 40,000 Montagnard men fought for the US Army against the invading North Vietnamese communists. They had a well-earned reputation for bravery and skill in combat, and fought alongside American Special Forces and SOG teams in crossborder operations in neighboring Asian countries. However, after the US withdrew from Vietnam due to the Marxist ambitions of the Democratic politicians and "peace" movement, the Montagnards were left to fend for themselves when the communist North took over the South in 1975. Thousands were murdered by the invaders for a multitude of reasons (one of them being that most Montagnards adhered to some form of Christianity; religious practice is strongly discouraged by communist states). Those who weren't killed were forced to flee to neighboring Cambodia and Thailand (Laos had it's own related communist takeover at the same time). Those in Cambodia found little respite, because immediately following the end of the Vietnam War, Pol Pot's genocidal Khmer Rouge regime took power, killing over 2 million of his own people from 1975 to '79.
Fortunately, several hundred (and later thousand) Montagnards were given citizenship by the US government and were relocated, the majority immigrating to North Carolina, home of the US Special Forces ("Green Berets") and other Southeastern states. Although their population in 1975 was over 5 million, today that number has dwindled to about 1/10th that. However, due to some inner strength and steadfastnest among the Montagnard people, the future is bright as each year more are able to secure transport to the United States. Which is not to say that all of them want that, but to those who do... you're welcome.
"RT Vermont's Montagnard commandos fought valiantly alongside their American companions in January 1970. Although several were killed, they died as heroes and are forever in the memories of those they served alongside with."