PoD: Watergate doesn't happen and the US continues a flow of arms to South Vietnam, in the long run it will result in a victory in Vietnam.
Watergate does not occur. Nixon sends more arms to South Vietnam along with advisors to train the ARVN which results in a much more prepared ARVN.
North Vietnam attacks South Vietnam. After the Second Battle of Hue morale in the ARVN begins to drop. Viet Cong attacks outside Saigon leading to several hundred dead. Other Asian countries begin sending arms and volunteers to South Vietnam to support the South. South Vietnam continues a strategic withdraw from the north of the country. In early summer the first volunteers arrive, several corps from South Korea, ex-patriots from Cambodia and a brigade of soldiers from Thailand.
A Viet Cong attack in Saigon kills the President and Vice President, with this sudden lack of leadership General Van Minh and his subordinates take control in a military coup. General Van Minh declares state law and rounds up guns from the population on the promise they will be returned once the war is over. President Reagan announces a slow withdraw of US advisors from South Vietnam.
Throughout Summer the RVNAF begins bombing raids of the Ho Chi Minh "Highway". Rockets attacks destroys sections of the roads while cluster bombs from RoK and RVNAF F-4 Phantoms destroy even larger sections of the road. The general staff of South Vietnam begin planning a counter offensive to retake Hue City from the NVA and to help the struggling 7th RoK Volunteer Corps trapped inside.
In late January the Allied forces launch Operation Southern Tet, this begins with a swift armored assault from Da Nang to retake Hue City. For three weeks Allied troops fight towards retaking Hue City. RoK troops in Hue City itself begin to starve as the Allies advance north. South Vietnam begins begging the world for more equipment than the US can give them. The people who responded was Britain and Australia. Britain sent a Asian Volunteer Corps made up of soldiers who would prove Britain "could win wars". Australia sent a volunteer brigade made up of men who had nothing left and pledged to defend Australia from communism. In Late Spring the first Anglo soldiers arrive under the cover of Indonesian and Malaysian soldiers (these two nations were sending troops as well). The ARVN manages to set up defenses around Saigon with the help of the British soldiers. Operation Southern Tet fades away into Operation Scorpion, repeated attacks on the NVA defenses. ARVN and RoK troops manage to cross the river with Australian aircraft backing them.
The Second Battle of Hue was becoming bloody battle of attrition. The NVA was determined to hold all land they had conquered in a bid to unite Vietnam. President Reagan continued a steady flow of weapons while quietly instructing the CIA to disrupt North Vietnam. China continued a flow of arms to North Vietnam but was beginning to get distracted with turmoil at home. Soldiers from Thailand and other nations continue to pour into South Vietnam. General Van Minh in coordination with the Cambodian ex-patriots launch a invasion of Cambodia sparing few armored vehicles for the invasion. Anglo forces patrol the countryside while the Asian troops fight the main war. Laos is bombed for the first time by Allied aircraft since the American bombing campaign stopped in 1973. In Cambodia the ex-patriots blitz through the countryside aimed at retaking the capital from Pol Pot. For early summer the Second Battle of Hue dies down as the 7th RoK had been reached after 20,000 killed. The Allies focus on fortifying the city while maintaining a supply rout to it. Another Viet Cong attack on Saigon results in a fiasco of violent terrorist attacks on local shops and guard posts. Anglo forces in Vietnam also begin increasing little by little into Summer. The NVA launches another attack towards Hue City but fails with nearly 300,000 killed. Allied bombers start pounding Hanoi and other major North Vietnamese cities from Da Nang. Unlike in the Tet Offensive Da Nang is now more secure. Canadian troops begin to land here. The Northern government refuses to accept defeat and announces a surrender plan for the South. In Cambodia the ex-patriots and ARVN armor reach the capital after a short but bloody fight against Cambodian forces on the border. The battle rages on through the whole year.
The ex-patriots retake the Cambodian capital and execute Pol Pot. Thai troops advance from Thailand itself and mop up the remaining Cambodian communists and the Khmer Rouge are rounded up and shot. Cambodia declares war on North Vietnam. Cambodian forces are rushed into South Vietnam. Laos begins a invasion of Cambodia to reinstall a communist country. South Vietnam declares war on Laos. ARVN soldiers and Cambodian soldiers counterattack against Laotian and a NVA offensive. From the stronghold at Hue City, ARVN and RoK forces push out from Hue City to retake parts of the countryside. Viet Cong forces in the Mekong Delta are starved into submission after a series of raids and rationing of the local population. Thailand launches a surprise attack on Laos scoring several victories and diverting much of the Laotian army to defend against Thailand. NVA troops are also diverted to defend against Thailand. The Viet Cong in the center of South Vietnam have effectively cut the nation in half. The Allies in summer launch a large invasion of Central South Vietnam and crush the Viet Cong resistance while implementing rationing tactics to stop any remaining resistance attacks.
The Allies planned to take the fight to were it was never since the late 50s, North Vietnam itself, and with the inclusion of Laos into the war, them too. The ARVN rebuilt its armored strength after the massive operations of 1976 and early 1977. The RVNAF took over the news channels as Allied bombers pelted Hanoi and Vientiane. RVANF bombers include several US B-52s and more numerous smaller tactical bombers like the B-47, B-58, and left over Canberra's. The bombing campaign flattens the communists industry and succeeds in flattening Laos and North Vietnam's capitals. The Naval campaign was one of confusion. North Vietnam's navy was small and made up of torpedo boats and obsolete Chinese warships. The VNN was sitting with ships given by the USA and UK. The Southern navy also had the Thai and South Korean fleets at its disposal. While the inland cities were pounded by bombers, the Allied fleet entered the infamous Gulf of Tonkin and bombarded North Vietnam's coast while helicopter raids destroyed many villages. To keep some of the troops entertained the Rolling Stones were going back to Britain the long way and were asked by the ARVN high command to tour the front starting in Saigon and heading to Da Nang then Hue City, then down through Cambodia and on a plane to Britain.
On January 20th the first ARVN tanks rolled past the DMZ and the old fire bases dotting the northern border. Operation Tet 2 was on the move. In the sky's Operation Tropic Thunder continued while Operation Acoustic had Southern Agents spread propaganda throughout North Vietnam. Allied forces in Laos quickly subdued the first resistance. Laotian aircraft launched a aerial attack on Bangkok and Saigon. Allied forces quickly march through the communist nations, North Vietnam's army is overwhelmed with fighting a defensive war. China briefly enters the war but backs down. Fighting in southern North Vietnam and Laos is brutal. Throughout spring and summer allied forces get 500,000 killed, wounded, missing, or captured. Fighting would also include wide scale armored warfare, more like armored guerrilla warfare. Ambushes caused the most allied deaths in North Vietnam.