All law was and is a fiction. Nothing can stop a murderer murdering you.

Well, try. I'm joking- don't.

Laws are enforced by sovereign countries that have police and courts etc. "International law" has "laws" (well very few if any) with no sovereignty. That's what makes it fiction. It's just newspeak to make people think that there are laws that exist outside the system of countries, and there aren't, at least no binding ones that countries can't and don't override. That's not a law.

Ofcourse laws, like any other human constructs, are invented by us and don't have independent existence.

When I drive to work here in Canada the "international police" stopping me for violating the "international traffic laws" is really not a concern.