Argentina invaded the archipelago without issuing an ultimatum or declaration of war. The british responded with military force, but also never issued a formal ultimatum or declaration of war. The argentinians had no formal bilateral alliances at the time. The British had several such, but chose not to make use of them.
Why exactly didn't the Thatcher administration issue an ultimatum or declaration of war? Could they have plausible done so? What would be the consequences if they had?
If the UK was formally in a defensive war would any of their allies have offered real or symbolic assistance?