Indonesia, Malaysia, the Philippines, Singapore and Thailand sign the Bangkok Declaration, founding the Association of Southeast Asian Nations.
North Vietnamese forces besiege the US Marine base at Khe Sanh in Quảng Trị; US forces abandon the base in July.
North Vietnamese and Viet Cong forces attack more than 100 cities and towns in the South; despite heavy losses, the offensive erodes US public support for the war.
US soldiers of Charlie Company kill hundreds of unarmed civilians at Sơn Mỹ, Quảng Ngãi; the killings become public in 1969.
After the failed 30 September Movement coup, the army and militias kill hundreds of thousands of alleged communists, paving the way for Suharto's rise.
A sustained US aerial bombing campaign against North Vietnam.
Two battalions of US Marines land at Đà Nẵng, the first American ground combat units deployed to Vietnam.