On November 23, 2010, military troops from the Republic of Korea (ROK, or South Korea) and the United States conducted war-simulation exercises, dubbed “Hoguk” [“Defend the State”], a massive joint endeavor involving 70,000 soldiers, 600 tanks, 500 warplanes, 90 helicopters, and 50 warships. It was slated to take place over a period of nine days.
… Amid the recent hostilities, modest mitigating gestures have emerged, though compromised by a confrontational war footing in the region. North Korea issued a statement calling the civilian deaths “very regrettable,” but it also criticized South Korea for creating what the North called “a human shield by placing civilians around artillery positions and inside military facilities.” On Nov. 29 South Korea canceled a series of scheduled artillery drills from Yeonpyeong Island, offering no explanation for the change. The massive US-ROK joint war exercises did resume in the Yellow Sea (or West Sea), but they have taken place outside the immediate zone of contested waters, staged approximately 125 miles south of the NLL.
Read more about this conflict from the National Campaign to End the Korean War here : Korea Crisis Fact Sheet.