From STRATFOR:
A South Korean ship has been sunk in the vicinity of the maritime border with North Korea. While details are sketchy, initial reports suggest that some South Korean naval ships had been involved in combat with an unidentified ship in the area immediately preceding the incident. Other reports suggest that the ship was struck by a torpedo. Yet another indicates a stern explosion.
Tensions between the two Koreas have always been at least moderately high, but previous governments in the South have tended to seek a rapprochement. That warming has cooled significantly in recent months; one result has been occasional naval skirmishes.
There are three issues to keep in mind when evaluating the potential for an inter-Korean conflict. First, the South Korean army, air force and navy are far better equipped and run than the North's, despite the North's numerical superiority when it comes to men in uniform. Stratfor has little doubt that the South could ultimately prevail in a military conflict.
But – and this is the second issue – it would come at a massive cost. The North maintains many thousands of artillery emplacements within range of Seoul. So while the South's military is superior by most measures, the North could quite easily decimate the South's capital and largest city. Roughly one in four South Koreans live in Seoul.
Third, the South Koreans are not alone. Despite recent shifts in American military posture, the United States still maintains 25,000 troops in South Korea – so an inter-Korean conflict immediately escalates to a global issue.