This situation is easy to understand if you ever played Civilization. You end up in war with some small nation on the other side of the world, usually because of alliances, but it's too much trouble to actually get your armies all over there so you ignore the whole thing.
@Kissamies Haha! I love this. You are absolutely right. "I'm technically in war wit Japan, but they have just one crappy city and are half way across the map. Nah. Why bother."
I have been told that Berwick-Uopn-Tweed is still at war with Germany. Apparently it was specifically included in the declaration of war, but not in the peace treaty.
@fiendishrabbit That makes it a lot easier to understand.
I mean, Denmark probably has a War room in his house, with a big board listing everyone he's currently at war with. Sweden of course having a hotkey or something. And then Denmark looks at this board to check who he's currently at war with. And there he see the danish flag. And he thinks "Well, this is the danish war room, so a danish flag is quite natural to have".
Same as Montenegro vs. Japan. (1904-2006)
Actualy, as Russian-Japanese war started, Montenegro also declared war, and few men joined the Russian forses. Russia lost the war 1905, but Montenegro didn't signed peace threaty, joined Kingdom of SHS (later Yugoslavia) and... forgot to sign it. Until 2006. when Montenegro declared independence.