South and North Korea are apparently trading artillery fire after North Korea shelled the South Korean island of Yeonpyeong in the Yellow Sea. Geography always matters in these things:
Yeonpyeong Island is right on the DMZ between North and South Korea and is among disputed islands in the Yellow Sea. Although not shown on this map, Seoul, South Korea's largest city and capitol, is right there on the northern border too, well within range of North Korean artillery.
North Korea is a basket case, unable to feed its own people, and in the midst of a succession crisis with national leader Kim Jong Il apparently in ailing health. So they are capable of anything. You can tell a lot from the language they used in today's press release: "The revolutionary armed forces of the DPRK standing guard over the inviolable territorial waters of the country took such decisive military step as reacting to the military provocation of the puppet group with a prompt powerful physical strike." This is a country that is divorced from reality.