<P> The Việt Cộng created an urban front in 1968 called the Alliance of National, Democratic, and Peace Forces . The group's manifesto called for an independent, non-aligned South Vietnam and stated that "national reunification cannot be achieved overnight ." In June 1969, the alliance merged with the NLF to form a "Provisional Revolutionary Government ." (PRG) </P> <P> The Tet Offensive increased public discontent with American participation in the Vietnam War and led the U.S. to gradually withdraw combat forces and to shift responsibility to the South Vietnamese, a process called Vietnamization . Pushed into Cambodia, the Việt Cộng could no longer draw South Vietnamese recruits . In May 1968, Trường Chinh urged "protracted war" in a speech that was published prominently in the official media, so the fortunes of his "North first" fraction may have revived at this time . COSVN rejected this view as "lacking resolution and absolute determination ." The Soviet invasion of Czechoslovakia in August 1968 led to intense Sino - Soviet tension and to the withdrawal of Chinese forces from North Vietnam . Beginning in February 1970, Lê Duẩn's prominence in the official media increased, suggesting that he was again top leader and had regained the upper hand in his longstanding rivalry with Trường Chinh . After the overthrow of Prince Sihanouk in March 1970, the Việt Cộng faced a hostile Cambodian government which authorized a U.S. offensive against its bases in April . However, the capture of the Plain of Jars and other territory in Laos, as well as five provinces in northeastern Cambodia, allowed the North Vietnamese to reopen the Ho Chi Minh trail . Although 1970 was a much better year for the Việt Cộng than 1969, it would never again be more than an adjunct to the PAVN . The 1972 Easter Offensive was a direct North Vietnamese attack across the DMZ between North and South . Despite the Paris Peace Accords, signed by all parties in January 1973, fighting continued . In March, Trà was recalled to Hanoi for a series of meetings to hammer out a plan for an enormous offense against Saigon . </P> <P> In response to the anti-war movement, the U.S. Congress passed the Case--Church Amendment to prohibit further U.S. military intervention in Vietnam in June 1973 and reduced aid to South Vietnam in August 1974 . With U.S. bombing ended, communist logistical preparations could be accelerated . An oil pipeline was built from North Vietnam to Việt Cộng headquarters in Lộc Ninh, about 75 miles northwest of Saigon . (COSVN was moved back to South Vietnam following the Easter Offensive .) The Ho Chi Minh Trail, beginning as a series of treacherous mountain tracks at the start of the war, was upgraded throughout the war, first into a road network driveable by trucks in the dry season, and finally, into paved, all - weather roads that could be used year - round, even during the monsoon . Between the beginning of 1974 and April 1975, with now - excellent roads and no fear of air interdiction, the communists delivered nearly 365,000 tons of war matériel to battlefields, 2.6 times the total for the previous 13 years . </P> <P> The success of the 1973--74 dry season offensive convinced Hanoi to accelerate its timetable . When there was no U.S. response to a successful communist attack on Phước Bình in January 1975, South Vietnamese morale collapsed . The next major battle, at Buôn Ma Thuột in March, was a communist walkover . After the fall of Saigon on April 30, 1975, the PRG moved into government offices there . At the victory parade, Tạng noticed that the units formerly dominated by southerners were missing, replaced by northerners years earlier . The bureaucracy of the Republic of Vietnam was uprooted and authority over the South was assigned to the PAVN . People considered tainted by association with the former South Vietnamese government were sent to reeducation camps, despite the protests of the non-communist PRG members including Tạng . Without consulting the PRG, North Vietnamese leaders decided to rapidly dissolve the PRG at a party meeting in August 1975 . North and South were merged as the Socialist Republic of Vietnam in July 1976 and the PRG was dissolved . The NLF was merged with the Vietnamese Fatherland Front in February 1977 . </P>

What name is given to the series of roads used by communist forces during the vietnam war