Source: U.S. Department of Defense
quote: The threat is the latest in a series of jabs between the U.S. and the defiant Asian military dictatorship. Following its decision to scrap the armistice, the U.S. conducted war games in SK. NK responded by cutting a key phone line used as one of the only diplomatic channels between the North and the South. In an apparent response to the line cutting, the U.S. proceeded with a test of B-2 Spirit stealth bombers over North Korea, which according to U.S. Forces Korea "demonstrates the United States' ability to conduct long-range, precision strikes quickly and at will."
quote: Letting your Airforce enter the Airspace of an enemy country isn't exactly known as softspoken diplomacy. The above chain of events is the exact definition of an escalation, whenever NK barks, the US and SK bark back. Because everybody knows that the best way to react to a idiot waving his gun angrily is to wave your own gun angrily back at him.