There are said to be 600 million barrels of
proven reserves, and exploration will probably reveal more.
Many Americans definitely lost. Some made oodles of money.
Some went south to be with family members sundered by the failure of America to honor the Geneva accords. The north-south separation was supposed to be temporary, but the oil was largely in the south, and that had to be sequestered for western business.
Roman Catholics fled the north at the urging of their bishops. Religious folks will act against their own best interests if they can be convinced that it will earn them pie in the sky, by and by, when they die. Since they already believed ridiculous nonsense, such conviction was easily secured.
To the extent that foreign troops were driven out the Vietnamese won.
Arms dealers in the U.S. made lots of money, and could be said to have won.
The common folk on both sides lost much, and are still losing.