In modern public international law, a declaration of war entails the recognition between countries of a state of hostilities between these countries, and such declaration has acted to regulate the conduct between the military engagements between the forces of the respective countries.
Indenfor folkeretten medfører en krigserklæring en erkendelse af fjendtlighederne mellem disse lande, og sådanne erklæringer skulle regulere ledelsen af militærengagementer mellem de respektive lande.