Regarding North Korea, it seems like it is a national decision instead of an international decision. There have been cases where trade was allowed to occur with North Korea and it was North Korea which chose to close the program.

Even now, North Korea could theoretically force a more open travel system with Russia and North Korea chooses not to. Hell, North Korea probably could get a peace treaty out of Trump and chooses not to.

I really doubt we're the only sentient life but we'll never meet any is my bet. The observable universe is mind bogglingly huge. The unobservable is so much bigger. So many stars, so many planets.

I have also had the thought that aliens might be offended by all the media humans have made about aliens

Which sequel trilogy? 1-3, or 7-9?