While there were plenty of other sources behind the concept, one can certainly trace the ICC back through the egregious show trials at Nuremburg and Tokyo and on to the odious Wilson's pet League of Nations.
Wilson's whole notion that there must be something beyond "might makes right" in international law is one of those things that sounds great over a bong in a dorm room at 3AM but doesn't have any basis in reality. The WWII Allies could have tried and sentenced Hitler in absentia, but it wouldn't have meant anything until you sent Joe and Tommy and Ivan into the rubble of a bombed-flat Germany to get him. And once you've done that, any goofy trials charging him with being a Very Naughty Boy are just silly. You don't need any elaborate legalizing when standing over the prostrate foe; you toss the sword on the scales, say "Vae victis!" and be done with it.
Anyhow, given the ample historical precedent we've set, it looks like the Hague is working up the nerve to see if it can hoist us by our own petard. Somewhere General Homma is laughing ruefully.