In the nineteenth century, French colonists named the mountain range that extends through the center of the Indochinese peninsula the Annamese Cordillera. The Vietnamese, who had settled Vietnam centuries earlier, knew the range as the Truong Son. In the 1960s and 1970s, American GIs referred to the portion of the Truong Son within South Vietnam as the Central Highlands or simply the highlands.
The cordillera possesses a vast and varied landscape of high, imposing peaks, dark jungles, grass-covered plateaus, and fast-running rivers. The mountain range stretches southward in an 800-mile arch from its origins in Laos to its termination northeast of Saigon.
The cordillera has no uniform width or elevation. In central Vietnam, where the Demilitarized Zone (DMZ) once separated the Democratic Republic of Vietnam (North Vietnam) from the Republic of Vietnam (South Vietnam), the cordillera extends from the edge of the coastal plain westward for seventy-five miles before ending in a forested plateau. Further south, the cordillera widens out. On the outskirts of the town of Cam Ly, the undulating mountains roll on for 175 miles until descending from the heights of the Plateau des Bolovens to the banks of the milky brown Mekong River at Pakse, Laos.
Looking west from Danang, the Truong Son reveals a hodgepodge of high and low peaks. Ngoc Linh is one of the cordillera’s tallest mountains; it straddles the border between Kontum and Quang Nam provinces. Ngoc Linh stands 8,366 feet tall and is located in an old-growth forest northeast of Dak To. Another cluster of high peaks can be found west of Nha Trang, where a steep escarpment rises abruptly from the lowlands. But across the cordillera, high, dramatic peaks are the exception rather than the rule. The majority of mountain tops are no higher than 3,000 feet – a testament to their great age and the erosive power of centuries of monsoonal rain.
In the middle of the cordillera between Ban Me Thuot and Pleiku, the terrain is predominately flat. Here, low hills and knolls are interspersed with level plains. Rather than jungle vegetation, the plateau country is blanketed by elephant grass and short, thin trees. This expansive interior region is actually a series of plateaus. The French referred to these tablelands as the Plateau du Kontum, Plateau du Darlac and the Plateau du Mnong.
The plateau country acquired a strategic significance during the first and second Indochina wars. In the 1950s and 1960s, American military analysts concluded that whoever controlled the plateau region would determine the future of South Vietnam.
The Americans feared that a Communist army in possession of the plateau country would have the ability to attack South Vietnam simultaneously on three fronts – eastward into the heavily-populated coastal plain, southward toward Saigon, and westward into Cambodia. From Cambodia, a military force could swing to the east and push into Saigon. Not coincidentally, during the Communist’s Spring Offensive of 1975, the North Vietnamese Army and Vietcong focused their initial military efforts on the plateau country. When Communist infantry overran the Plateau du Kontum around Pleiku and the Plateau du Mnong near Ban Me Thuot in March of that year, South Vietnam’s fate was sealed.
Along the entire length of the cordillera, runoff from heavy rains has eroded deep, sun-deprived valleys. Rivers flow either east or west depending on where they originate in relation to the cordillera’s spine. East-flowing rivers are short and fast, falling rapidly from the highlands to the South China Sea. West of the divide, the streams descend more slowly, and along more circuitous paths, to an eventual juncture with the Mekong River.
The Ben Hai is a notable stream flowing east from the cordillera. It begins in the remote hill country north of the old U.S. Marine base at Khe Sanh. From there, it hurriedly drops to the coastal plain. Once down in the rice paddy country, the river slows and widens out. Before reaching the South China Sea, the Ben Hai runs deep and wide. The Ben Hai is only thirty-seven miles long from start to finish. Between 1954 and 1975, the river acted as the demarcation line between North and South Vietnam.
South of the Ben Hai is the Thach Han River. Its headwaters are also located near Khe Sanh. This river tumbles eastward through a land of high, round peaks and dense jungle. Near Khe Sanh, it rushes over a rocky riverbed fringed by steep, stone walls. Old French Route 9 parallels a segment of the Thach Han’s northern margin. In places, the razor-thin, two-lane highway clings to a precarious ledge situated high above the valley floor. Beyond Quang Tri City, the waters of the Thach Han mingle with those of the Meiu Giang to form the Cua Viet River. The Cua Viet spreads out into a sandy, flood-prone delta before dumping its waters into the South China Sea.
For centuries, Vietnam’s east-flowing rivers, such as the Ben Hai and Cua Viet, acted as obstacles to north-south travel and communication. The streams did not make human movement impossible, but they did impede it, especially during flood periods, which frequently came on the heels of the northeast monsoon. In the often-isolated pockets of territory located between the lowland rivers, the rural population became parochial, xenophobic, self-reliant, and distrustful of centralized authority.
The rivers were not the only physical feature hindering the integration of Vietnam. The cordillera acted as a major obstacle to the coupling of the lowlands with the highlands. The Vietnamese, and later French, found it impossible to fully dominate the cordillera. Terrain, tropical diseases, poor soils, a dearth of roads, and the hostility of the cordillera’s indigenous inhabitants kept the Vietnamese and French largely restricted to the lowlands. As a result, the cordillera remained in the hands of the mountain tribes, (known collectively by the French term “Montagnards”) until well into the twentieth century.