It always boils down to the US ignoring international trade and laws in their favor. As you said there is nothing illegal about two countries trading. The idea the US should have a say is deeply undemocratic and frankly anti-human as well, but that's just the US for you.

This podcast does a great job on highlighting how the media plays its role in justifying the imperialism too:

https://citationsneeded.libsyn.com/shadow-fleets-sanctions-w...