Declared and Undeclared Wars

Occasionally, people characterise foreign military interventions as “undeclared wars”. It is not entirely clear what is the meaning and value of such a qualification, but it seems that they want to add an extra weight to their condemnation. Still, does it have legal significance? At times, international law demanded that States issued a declaration of war before the commencement of hostilities but the obligation was mostly ignored for varied reasons. Notably, between two world wars, States avoided certain legal obligations (e.g. the prohibition to use war, the rules of warfare) by not declaring or otherwise recognising a state of war. After the Second World War, considering the earlier abuses, States redesigned the international legal regulations in a way that the declaration of war became practically irrelevant when it comes to the legality or illegality of the use of armed force, or to the application of law.