Why is International Law Binding?

Many writers believe that international law is precatory but not "binding" in the way domestic law is binding. Since international law derives from the practice of states, how is it that what states do becomes what they must do? How do we get bindingness or normativity out of empirical fact? We have to avoid the Humean fallacy of attempting to derive an ought from an is. Yet we can find in nature at least one norm that is compelling: the norm of survival. This norm is hardwired into our brains through evolution. It is also hardwired into the international legal system that has survived for four thousand years. In every dispute or controversy, the international legal system weighs in on the side of peaceful and stable resolution - simply because that is in the system's interest of self-perpetuation. In sum, it is international law itself that selects from state actions those actions most conducive to the peaceful resolution of disputes and formulates them as rules and precedents of the system.