Hi there!

I've written plenty about the military aspect of the defeat, out of a counterinsurgency focus. You can read this here.

Now, as I mentioned, this is merely the military aspect and does discount other factors in the American defeat (US politics, lack of support at home and South Vietnam issues also playing a big role).

I'd also like to mention that there has been some dissenting voices about my above assessment of what led to the American military defeat in South Vietnam. Historian Gregory Daddis in his book Westmoreland's War: Reassessing American Strategy in Vietnam (Oxford University Press, 2014) argues that the US military command as well as its regular officers were familiar and had studied counterinsurgency extensively in the pre-Vietnam years and that the defeat in Vietnam was not because of the lack of counterinsurgency but rather because the American strategy in Vietnam (yet, Daddis argues, still with a very prominent focus on counterinsurgency) and the political goals were difficult to achieve since they were hard to properly define into achievable goals. Daddis also puts out an argument regarding how detrimental the South Vietnamese government was to the American war effort in South Vietnam.

I personally do not adhere to the view of Daddis whose arguments in the book are quite unconvincing (if counterinsurgency was indeed a major part of American strategy, then why wasn't more time spent on it as opposed to the large divisional offensives?), but who still makes a very important point regarding the political goals set out by the American government. There also seems a will in Daddis to make a scapegoat out of South Vietnam which seems rather unfair. The book as you can imagine has created some controversy amongst Vietnam War scholars with some praising it and some being far more critical than yours truly, yet it is books like these which challenges and drives this area of study further.