Also "war" is the thing that happens between parties above which no legal frame or enforcement institution exists. Countries. There's no actual "international court" (there's the UN one, but it has no powers). This is why wars happen. So in fact, mentioning wars defeats your own point - yes, people will literally kill each other like savages when no legal repercussions exist. Wars show that.

Because we have no world government, we can only apply mitigation strategies like sanctions, diplomacy, economic interdependence. These work, but only until a true scarcity occurs, where taking someone else's stuff is a solution. Then it's back to wars.