US politics are usually terrible for other countries. Their national interest is always put before anything and more worrying - before anyone. They do have a long tradition of not caring at all for anything other that the electoral results. In the case of Iran sanctions, it must be noted that Iran is trying to arm themselves with atomic bombs. No wonder they are sanctioned.
As yourself why Iran or North Korea is not invaded yet. What makes them different, when compared to Libya, Afghanistan or Iraq. These two countries are rumored to have nuclear weapons and the ICBMs that can deliver the nukes. Americans are bullies and they showoff their power only against weak countries. A war against either Iran or North Korea can completely destroy the American economy on top of hundreds of thousands of American casualties. The US became a superpower after the WW2, because they stayed out of the conflict until the last phase.