The civil war in Vietnam after the commencement of large-scale US military involvement in 1964. Guerrilla activity in South Vietnam had become widespread by 1961, in which year President Ngo Dinh Diem proclaimed a state of emergency. Continued communist activity against a country perceived in the USA as a bastion against the spread of communism in south-east Asia led to increasing US concern, and after an alleged North Vietnamese attack on US warships in the Gulf of Tonkin in 1964, President Johnson was given congressional approval (Tonkin Gulf Resolution) to take military action. By the summer of 1965 a US army of 125,000 men was serving in the country, and by 1967 the figure had risen to 400,000, while US aircraft carried out an intensive bombing campaign against North Vietnam. Contingents from South Korea, Australia, New Zealand, and Thailand fought with the US troops. Although communist forces were held temporarily in check, the war provoked widespread opposition within the USA, and after the Tet Offensive of February 1968 had shaken official belief in the possibility of victory, the bombing campaign was halted and attempts to find a formula for peace talks started. US policy now began to emphasize the ‘Vietnamization’ of the war, and as increasing efforts were made to arm and train the South Vietnamese army, so US troops were gradually withdrawn. Nevertheless, US forces were still caught up in heavy fighting in the early 1970s and the bombing campaign was briefly resumed on several occasions. US troops were finally withdrawn after the Paris Peace Accords of January 1973, but no lasting settlement between North and South proved possible, and in early 1975 North Vietnamese forces finally triumphed, capturing Saigon (the capital of South Vietnam; renamed Ho Chi Minh City in 1976) on 30 April 1975. The war did enormous damage to the socio-economic fabric of the Indochinese states, devastating Vietnam and destabilizing neighbouring Cambodia (Kampuchea) and Laos.