The US has been a hypocrite since well before Vietnam, starting with slaughtering the People, and moving the People to reservations. When it comes to foreign policy, there have been all manner of doctrines where the US has tried to dictate what brand of government should be used, and which countries can colonize other countries.
In just the last 24 years, the US Government has taken some form of military action in quite a few countries with no declaration of war against those countries, as if we actually have some right to just do whatever we want in the name of "US National Security". Killing innocent civilians in Yemen, or Syria, etc., etc., is just wrong. We're told the actual targets are terrorists trying to kill us. This may or may not be true, but what is true is that our government has no problem lying to us, and covering up their duplicity and failures.