There is too international law. It’s established via countries with most nations signing on to it. And when all the big players sign on..it becomes defacto international law for the smaller nations that didn’t agree.
When countries like Russia, China, India, the United States, Israel, Ethiopia, Indonesia, Pakistan, Iran, Saudi Arabia, and Turkey don't actually recognize the ICC's jurisdiction (being non-Parties to the Rome Statute or those who haven't ratified it), I think it's safe to say that the ICC's jurisdiction is far from "de facto international law."
No they haven’t signed on....and that’s why this won’t happen.....
Russia does not recognize the ICC, and the US’s relationship with the court has been fraught, according to Human Rights Watch. Ukraine does not fully recognize the court either.....nor China nor Israel nor the US.
Countries want to have control over the prosecution of their criminals and do not want to have the input of the ICC.