The three-part frame (the unit's conceptual spine):
1. Jus ad bellum — the law governing the resort to force: the justice/legality of going to war (the just-war criteria: just cause, legitimate authority, last resort, proportionality of ends) — modernly: the Charter's prohibition + self-defence;
2. Jus in bello — the law governing the conduct of hostilities: humanitarian law (Unit 7) — applicable equally to both sides regardless of who started (the separation principle: the aggressor's soldiers are lawful combatants; the just side may not violate the laws with impunity — jus in bello's independence from jus ad bellum the twentieth century's hardest-won clarity);
3. Jus contra bellum — the Charter's terminology of prevention: the law against war — the prohibition regime + collective security + the dispute-settlement machinery (Unit 8) — the modern term capturing the system's design (Dinstein's coinage-family): no longer regulating war's how or why but excluding it.