Here is a interesting fact. Vietnam lost nearly million dead to US bombs and guns. That is more dead then any Muslim country has lost in the last 70 years. In other words Vietnam is the single biggest victim of US military power than any other country since WW2.
On the other hand Vietnam killed nearly 60,000 American military personnel. More Americans have died at the hands of Vietnamese then in any other war since WW2. If you count every American killed by every single Muslim country since WW2 the number is still 10 times less.
This means Vietnanese fought like lions and killed Americans on epic scale and the defeated them. No Muslim country has done this damage or fought so well or defeated the USA like Vietname did.
Although the other side of coin is Americans killed million Vietnames. By this measure the Vietnamese would be entitled to nurse the biggest hatred for America then any other. On the American side with 60,000 lost I could understand if America despised the Vietnames.
But why is it today the Vietnamese are such good friends with Americans who in turn also have a soft spot for Vietnam. Contrast this to the hate you see by many Pakistani's against USA when there is no historty of bloodbath like Viet/USA war.
The conspiracy theories can be disregarded, this requires actual studying of US-Vietnam ties post 1975, rather than amateur guesses.
The obvious elephant in the room is the US' changing interests and threat perceptions over the previous 50 years. Post WW2, the US' main priority was tackling the USSR and it's so called "Iron Curtain" in Europe and growing communist influence globally. This influence impacted South East Asia too, with North Vietnam's communist regime in place, so naturally it became a theatre for US ops when it tried re-integrating South Vietnam within its territory.
After the war, the USSR moved onto Afghanistan and again the US reacted there and we all know what happened. However, from the 90s onwards, it seems like after the US' objective of defeating the USSR was fulfilled, it then moved onto securing oil reserves and focusing on Muslim countries, primarily those who had oil. In 2008, we had the sub-prime mortgage crisis, which no doubt played it's part in limiting new US invasions in recent years. This period from 1980-2010, it seems plain as to why Vietnam was no longer near the forefront of the US' strategic calculus, since it effectively was not a country that resonated with the core issues the US saw it needed to deal with. From 2010 onwards, we have seen the emergence of China jockeying for the top of the totem pole with the US and in some aspects it arguably is even ahead on. Thus, in this backdrop, the US' interests converge to an extent with Vietnam's, in that containment of China is beneficial for both countries and working together may be help them achieve their national interests whilst trying to mitigate China as a threat.
Regarding casualties in the Vietnam campaign vs in current wars, let me preface this by stating that I am not a military expert, so if incorrect on details please correct me. For me 3 reasons stand out:
- Technology (lack of applicability of it in jungle warfare/no access to the modern advancements of today)
- Spec Ops utilisation
- Jungle warfare vs Urban and conventional warfare
Technology - this includes land, sea, air and space, given the environment of the war in Vietnam, it was in thick forests and jungles which made it easier for the sub-conventional warfare that the Viet Cong waged against the US. Primarily, focused on underground bases to avoid getting hit by fighter jets and attack helios and also to enable a stable base of operations, the Viet Cong were able to adapt using natural means and thus slightly nullified the advantage of technology the US had. Alternatively in AFG, the land is so barren and rocky, the initial invasion which employed the use of fighter jets to good effect given the easier topography as well as advancements in tech since the 70s, was easily able to occupy the major chunk of the land within a few weeks.
- Spec Ops Utilisation, a hallmark of US campaigns is to use special forces as a tip of the spear to accelerate progress. However, the war they were fighting was essentially defending against battle-hardened guerrilla fighters in their own conditions, rather than typical conventional armies using textbook methods. This was further exacerbated in the jungles where the element of surprise was with the Viet Cong rather than the US SFs.
- Jungle warfare, I think most of the US casualties may have been whilst operating in the jungles vs urban environments, where they could use their special forces and airforce to great effect.