Jus ad bellum is a Latin phrase that means right to wage war. This indicates a criterion that is consulted before engaging in war. This phrase concerns whether a war is conducted justly or if whether the entering into war is justifiable. An international agreement limiting the justifiable reasons for a country to declare war against another is concerned with jus ad bellum. The principles central to jus ad bellum are right authority, right intention, reasonable hope, proportionality, and last resort.