Should we worry?

The U.S. and South Korea put their military forces on high alert Thursday after North Korea renounced the truce keeping the peace between the two Koreas since 1953.

The North also accused the U.S. of preparing to attack the isolated communist country in the wake of its second nuclear bomb test, and warned it would retaliate to any hostility with "merciless" and dangerous ferocity.

Seoul moved a 3,500-ton destroyer into waters near the Koreas’ disputed western maritime border while smaller, high-speed vessels were keeping guard at the front line, South Korean news reports said. The defense ministry said the U.S. and South Korean militaries would increase surveillance activities.

Pyongyang, meanwhile, positioned artillery guns along the west coast on its side of the border, the Yonhap news agency said. The Joint Chiefs of Staffs in Seoul refused to confirm the reports.

The show of force along the heavily fortified border dividing the two Koreas comes three days after North Korea conducted an underground nuclear test and fired a series of short-range missiles.

The test drew immediate condemnation from world leaders and the U.N. Security Council, where ambassadors were discussing a new resolution to punish Pyongyang. President Barack Obama called it a "blatant violation" of international law.

In response, South Korea said it would join more than 90 nations that have agreed to stop and inspect vessels suspected of transporting weapons of mass destruction.

Then Anderson Cooper has an article on how South Koreans aren’t losing sleep over the threats. It’s not hard to understand if you put yourself in the shoes of a normal South Korean. After the two Koreas fought a war in the 1950s, the two sides have faced off in one of the world’s most hostile borders. And since that time, North Korea has made more than its share of threats against the South.

How many times has North Korea threatened war on the Korean peninsula since the two Koreas battled from 1950 to 1953? Just off the top of my head, I can recall at least three in the past decade.

North Korea seems to come out with belligerent statements every time joint U.S.-South Korean troops conduct their annual military exercises.

So what’s one more declaration of war?