There Is a War Already

North Korea accuses the USA of declaring war against them.

This is silly. North Korea and the USA are already at war with each other. They have been since 1950. There was a cease fire in 1953, but no peace treaty has ever been negotiated, much less signed.

You cannot really declare war on a state which you are already at war with, can you?

It is said that Andorra did not show up at Versailles in 1919 and never signed the peace treaty with Germany after the First World War, so when Andorra followed France and declared war in 1939, they found thenselves fighting two world wars simultaneously. This ended with a separate peace treaty in 1939 with regard to the First World War, while the Second World War was allowed to continue. This is an exception to the rule. The USA and North Korea should both know that there is, actually, a state of war between them. The question is rather who might break the cease fire first. I hope none of them do.