Vietnam was a really sucky situation. SOME people were encouraging US involvement in order to make money (a lot of it).
As I recall, the sales pitch which Our Masters, our politicians, and mostly our media kept trying to deliver was that we were fighting "Communism" in order to "Make the World Safe for Democracy". But, as I recall, that never really registered with most people.
But, in the end, we have become Communist, and we no longer have a real Democracy. None of the wars protected us. If fact, all the wars enabled this outcome: the more wars we fight the more we lost sovereignty, wealth, and even moral/intellectual compass. Clever moves by our Military Commanders, getting us to commit the suicide Franklin warned us about.
Again, I recommend you to http://wtfhappenedin1971.com/
And suggest you deeply ponder those charts. By the time Nixon closed the gold window, the US was less than six months away from being FORCED to declare national bankruptcy. ALL THE GOLD - WHICH OTHER COUNTRIES HAD ENTRUSTED TO THE US FOR 'SAFEKEEPING' - WAS GONE.
You cannot "win" a war which drives you into economic bankruptcy and then costs you your Constitution. No matter what "tech" you have, and no matter how well trained your soldiers are, and - actually - no matter how many battles you 'win', you are actually losing the whole while. The lessons of history are quite clear on this topic and littered with empires which tried and failed. The US is just the latest sad exampmle.
I think the US is actually perhaps the saddest example in all of human history. Our Constitution and Federation of independent states was remarkable. We got swindled. Perhaps we swindled ourselves.
Certainly, enough of us should have known better. We were EXPLICITLY WARNED against DOMESTIC enemies. First we were warned by the Founders. Then, Eisenhower warned us, again, in a remarkable farewell speech about the designs of the "military-industrial complex".
And then [someone] killed Kennedy.
And then [someone] sent us to Vietnam.
Probably not a coincidence that it happened that way.