Korean tensions increase over South Korean ship attack by North Korea. The U.S. has 28,500 troops defending South Korea and a treaty obligation to aid the South in the event of war with North Korea. This one could get very, very, bad! North Korea’s military capabilities, especially with their active nuclear weapons arsenal, make the worries over Iran’s nukes look like a tempest at a tea party (no pun intended!)
http://www.historyguy.com/korean_border_conflicts.htm