Late last week, a team of international investigators accused North Korea of torpedoing the Cheonan corvette in March, killing 46 sailors in one of the deadliest clashes between the two since the 1950-53 Korean War.
The United States still has about 28,000 troops in South Korea to provide military support. The two Koreas, still technically at war, have more than 1 million troops near their border.
U.S. military told to get ready in Korea standoff - North Korea- msnbc.com