I believe I proposed something like a "no executive" world government, where you had international laws, defined by treaties, and a commitment by some treaty signatories to "arrest" any state actor which broke them. If this coalition of "world police" (which are, of course, armies) were powerful enough, I believe this could lead to less lawbreaking by governments (from the USA to Zimbabwe). Note, the commitment is not to start wars/invade, but specifically to arrest e.g. presidents or generals. You can't do this without an army, but the objective is considerably different from invading, neutralising any opposing forces, and securing a place.
Of course, persuading people something like this is a good idea, your actual question, is just about the hardest problem I've ever thought about solving. I still don't really know where to begin, but I'm interested in teaching people epistemology before other things, as a means to halt the "post truth" stuff (which has been going on for years, not only recently!)
By the way, if anyone wants to work on these idea with me - I'm calling the concept "World Peace, Inc" in my head - please get in touch with me (clues in profile). I'd love for this to be my job rather than the hobby I don't have time for.