The Demilitarised Zone (DMZ) was created in April, 1954 as a result of the Geneva Conference ending the war between the Viet Minh and the French.  The DMZ extends 5 km north and south of the Ben Hai River and runs approximately 100 km from the South China Sea to the Laos border.  Originally proposed as a temporary demarcation line between the communist controlled north and the "democratic" south, the DMZ became the permanent border between North Vietnam and South Vietnam when the 1956 nationwide elections were cancelled due to the obvious imminent victory of Ho Chi Minh and the Communists.  Fearing the downfall of the South Vietnamese government to the powerful Communist Army of the North, the United States began sending military advisors, troops, supplies and weapons to the South Vietnamese government headed by president Ngo Dinh Diem. 
In an effort to supply the Viet Cong (South Vietnamese Communists) with troops and armaments, the North Vietnamese Army (NVA) created a series of interconnecting roads and trails (approximately 20,000 km in total) popularly known as the Ho Chi Minh Trail, which extended from North Vietnam to the South.  In an attempt to stop this flow of munitions, the United States and the Army of the Republic of Vietnam (ARVN, the South Vietnamese Army) created a series of bases along Route 9 (which parallels the DMZ appproximately 10 km to the south). 
This series of bases, mines and electrified fencing became known as the McNamara Line, named for the U.S. Secretary of Defense, Robert McNamara.  Some of the fiercest and bloodiest battles of the American War in Vietnam occurred along this line at places such as Khe Sanh Combat Base, The Rockpile, Camp Carroll, Con Thien Firebase and Doc Mieu Base. 
We spent our first day in Vietnam visiting the remains of these and other sites along the DMZ.  It was an educational and sobering experience best summed up by our Vietnamese guide, "A war with no winners."