There was a time during the 1960s when people thought that the continental shelf immediately offshore from Vietnam must be filled with oil--because U.S. stubbornness in Vietnam was inconceivable unless someone stood to profit immensely from the defeat of Ho Chi Minh.
Yet that oil was never found (although some may be someday in territory now effectively claimed by China). And were it to be found, the Vietnamese government would (judging by its behavior toward Nike) give Chevron more advantageous terms from extracting it than perhaps any other government on earth.
I think that most of the time U.S. foreign policy elites have no clue about what the long-run national interest (or the long run interest of the American bourgeoisie) is: recall that Kissinger's reaction to the Shah of Iran's pushing for a tripling of world oil prices in 1973 was that it would make his life easier--the Shah would be able to buy the weapons Kissinger wanted to give him to serve as a proxy opponent on the Soviet Union's southern border...
Brad DeLong