Our main destination for the day was the War Remnants Museum, primarily containing exhibits relating to the American phase of the Vietnam War (the Yanks didn't stick around for all of it). Now to build on my previous history lesson...
Vietnam was colonised in stages by the French between 1858 and 1887. The French went on to colonise much of this area in what became known as French Indochina. The Viet Minh was a Vietnamese national independence coalition formed in 1941. Led by Ho Chi Minh, the Viet Minh initially formed to seek independence for Vietnam from the French Empire. During World War II, Japan occupied French Indochina (with minimal resistance from France) and so the Viet Minh turned their attentions to opposing Japan; for this they received support and funding from the United States, China, and the Soviet Union (part of the Allies of World War II). When Japan surrendered in August 1945, Ho Chi Minh declared Vietnamese independence, was then key in the subsequent formation of the communist Democratic Republic of Vietnam (a.k.a. North Vietnam, with Hanoi as its capital), and his Viet Minh crew opposed the re-occupation of Vietnam by France. In response to this, France established a (non-communist) puppet government in Saigon, reoccupied Hanoi, and the French Indochina War followed. This war lasted about eight years from 1946 to 1955, and resulted in a Viet Minh victory and the French getting the hell out of Indochina.
Now to digress somewhat. After World War II, the United States and the communist Soviet Union emerged as rival superpowers (despite the success of their temporary wartime alliance against Nazi Germany). This set the stage for the Cold War. The US perceived communism as the largest post-war threat, and created a policy of "containment" which involved the use of military, economic, and diplomatic strategies to stall the spread of communism, enhance America's security and influence abroad, and prevent a "domino effect". The domino theory speculated that if one state in a region came under the influence of communism, then the surrounding countries would follow in a domino effect. The domino theory was used by successive US administrations during the Cold War to justify the need for American intervention around the world.
Now to tie this all together. The United States supported French efforts to retake the now-communist North Vietnam as part of their Containment policy to prevent the spread of communism. At the end of the French Indochina War 1956, Geneva Accords stipulated that Vietnam be temporarily separated into two zones: a northern zone to be governed by the communist Viet Minh, and a southern zone to be governed by the State of Vietnam (later the Republic of Vietnam, a.k.a. South Vietnam). The Geneva Accords also stipulated that a general election be held regarding total unification into one country. However, South Vietnam, with the backing of the US, refused to hold unifying elections claiming that Ho Chí Minh could not be trusted due to his affiliation with communism. This gave the Viet Minh the opportunity to march south to reunify the country by force. This plunged the country back into war - the Vietnam War. South Vietnam and the US against the North Vietnamese Viet Minh (and later the Viet Cong).
So while the North and the South saw this as a civil war over the reuniting of the Vietnam, the US saw it as the prevention of the spread of communism - their same reason for involving themselves in the earlier Korean War I believe. Anyway, I hope all that made sense (and is correct hehe) because it's taken me the best part of three hours to research it thoroughly.