"The Dane is coming!"
There was a bank robbery in Stockholm in 1973 called Norrmalmstorgsdramat, during which two people took four others hostage. As the situation progressed, the hostages started protecting the robbers. International coverage of the drama called it "Stockholm syndrome", and the term stuck.
"Danska"=the danish language, "dansk"= a danish person. The definite form of "danska" is "danskan" and the definite form of "dansk" is "dansken". Yes "a dane" is "en dansk", but you are refering to one person only, while "dansken" in this sentence is refering to the danes as a nation. So you can say "en dansk kommer" but it's not as intimidating. :)