Is this move by North Korea to nullify the armistice that's been in place since 1953 more symbolic than real?

We better hope so. South Korea, a modern country with a modern economy, could be severely damaged by a surprise attack. Seoul is within long range artillery of the North Korean army - they wouldn't even have to cross the DMZ to cause billions of dollars in damage.

CNN:

Despite the strong language, analysts say North Korea is years away from having the technology necessary to mount a nuclear warhead on a missile and aim it accurately at a target.

And, analysts say, North Korea is unlikely to seek a direct military conflict with the United States, preferring instead to try to gain traction through threats and the buildup of its military deterrent.

North Korea has called the annual training exercises "an open declaration of a war," but South Korea says it notified Pyongyang that the drills "are defensive in nature."

The United Nations Command notified the North Korean military on February 21 of the exercise dates, noting that Key Resolve is an annual joint exercise that is not related to current events on the Korean Peninsula.

The U.N. Security Council unanimously passed tougher sanctions against North Korea Thursday targeting the secretive nation's nuclear program, which followed successful missile and nuclear tests.

The North Koreans would be crazy to launch an attack. But how much faith do we really have in the rationality of the leadership clique? Who knows what might set them off? Counting on the North Koreans to act as other nations would is comforting but might not be realistic. We know so little about what makes them tick that a mistake in perception could lead to untwoard consequences.

Update from Thomas Lifson

Walter Russell Meade provides a highly plausible framework for understanding what's really going on, though as always with North Korea, a certain amount of uncertainty is built-in. In sum, China is tightening the screws on Pyongyang:

 Ask A Koreanblog is reporting that the coming sanctions are being accompanied by a recent Chinese crackdown on cross-border smuggling, which has sent the price of necessities soaring:

After its third nuclear test, the price of rice in Pyongyang jumped from 5,500 won per kilogram to 9,000 won per kilogram. The cost of other groceries likewise increased by around 70 percent.

That's potentially a big deal if true. The sanctions which just passed last week were some of the strictest imposed yet on the North-and these sanctions have almost certainly not started biting yet. The young Kim is still an untested leader, even in the eyes of his wretched, brainwashed countrymen, and a wave of nationwide privations to kick off his reign cannot be a welcome development.

It must be worrisome for the clique running North Korea to see China pressuring it. They know only one tool, historically: bluster and aggression, up to and including sinking vessels, shelling islands, shooting missiles, and exploding nuclear devices. They control the population of North Korea through intimidation. That is their mentality. It is no surprise that they treat the rest of the world this way, too.