A language is not a dialect with armed forces. Thats junk. Danish, Norwegian and Swedish are all comprehensible to someone who speaks one of the languages - in fact, you can only speak one of the languages because they are so similar. But as my mother points out, they aren't dialects of one language, they are different languages and thats in part because they originate in different variants of Old Norse.
Tell that to Plattdeutsch then.