International law is the attempt to apply the logic of law — binding norms, adjudication, enforcement — to the relations between sovereign states that have, by definition, no authority above them to enforce compliance. Its achievements are real: the prohibition on torture, the protections of the Geneva Conventions, the International Criminal Court's jurisdiction over war crimes. Its limits are equally real: enforcement depends almost entirely on political will, powerful states are far less subject to it than weak ones, and the gap between the law on paper and the law in practice is often where the most significant injustices live.
Each step builds on the last.