Earlier quoted context omitted.
International law was and is also a fiction. We have various conventions and agreements. https://en.wikipedia.org/wiki/International_law "In the 1940s through the 1970s, the dissolution of the Soviet bloc and decolonisation across the world resulted in the establishment of scores of newly independent states.[67] As these former colonies became their own states, they adopted European views of international law.[68] A…
All law was and is a fiction. Nothing can stop a murderer murdering you.
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.