"We are the world" was written and performed in 1985 as a way to raise money to help starving people in Ethiopia. North Korea has been known to suffer from food shortages, and its people are believed to be impoverished.
The video might be meant to say, "Hey, we're going to kill you unless you give us food."
But really, it's more serious than that. This New York Times blog explains what the film says.
North Korean leader Kim Jong Un does seem to have a contradictory approach to the United States. He acts belligerently and defies U.S. efforts to get him to back off his nuclear weapons program. Then he turns around and steals Disney characters for a strange program broadcast last year on national TV.
Even this film isn't original. It was stolen from the video game, “Call of Duty: Modern Warfare 3.”
There can be no denying that North Korea considers itself the mortal enemy of the United States. Such clumsy pieces of propaganda draw instant laughs over here, but they are deadly serious in intent.