Vietnam War: In response to U.S. President Lyndon B. Johnson's call for "more flags" in Vietnam, Philippine President-elect Ferdinand Marcos announces he will send troops to help fight in South Vietnam.

Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about 331,000 square kilometres (128,000 sq mi) and a population of over 100 million, making it the world's fifteenth-most populous country. One of two communist states in Southeast Asia, Vietnam shares land borders with China to the north, and Laos and Cambodia to the west. Its capital is Hanoi and its largest city is Ho Chi Minh City.

Ferdinand Emmanuel Edralin Marcos Sr. was a Filipino lawyer, politician, and kleptocrat who served as the tenth president of the Philippines from 1965 to 1986. Ruling the country as a dictator under martial law from 1972 to 1981, he granted himself expanded powers under the 1973 Constitution; he described his philosophy as "constitutional authoritarianism". He was eventually deposed in 1986 by the People Power Revolution and was succeeded as president by Corazon Aquino.

South Vietnam, officially the Republic of Vietnam, was a country in Southeast Asia that existed from 1955 to 1975. It first garnered international recognition in 1949 as the associated State of Vietnam within the French Union, with its capital at Saigon. Since 1950, it was a member of the Western Bloc during the Cold War. Following the 1954 partition of Vietnam, it became known as South Vietnam and was established as a republic in 1955. South Vietnam was bordered by North Vietnam to the north, Laos to the northwest, Cambodia to the southwest, and Thailand across the Gulf of Thailand to the southwest. Its sovereignty was recognized by the United States and 87 other nations, though it failed to gain admission into the United Nations as a result of a Soviet veto in 1957. It was succeeded by the Republic of South Vietnam in 1975. In 1976, the Republic of South Vietnam and North Vietnam merged to form the Socialist Republic of Vietnam.