Explain the sources of IHL: the Hague-and-Geneva branches, custom, and the Martens Clause.

International humanitarian law (IHL) — the law of armed conflict: the body of rules which, in times of war, protects persons who are not (or no longer) participating in the hostilities, and restricts the means and methods of warfare. The classic definition's core: IHL does not ask whether the war is lawful (the jus ad bellum question — the UN Charter's world) but how it must be fought (the jus in bello). The scope's faces: the armed conflicts only (the applicability threshold of U2); the parties bound (states, organised armed groups — and the individuals through criminal responsibility); the temporal-and-territorial scope (the conflict's duration-and-space). The aims (the ICRC's formulation): limit suffering, preserve humanity in the midst of war.