Every day hundreds of South Korean workers make their way across a special border crossing to work at a North Korean industrial complex that is jointly run by both nations. But not today. Authorities in the North have shut down the crossing and blocked Southerners from entering, taking their ongoing feud from the level of idle threats to very real action.
The Kaesong Industrial Complex sits on the North side of the border and is pretty much the only legitimate avenue of partnership between the two nations. Yet, because they've recently made it their mission to antagonize the South at every turn, this move is one of few they have (short of actual war) that can actually hurt their neighbors economically. (But not as much as it hurts the North.)
Authorities in Pyongyang have shut down the complex before, temporarily preventing some South Korean workers from returning home back in 2009. That standoff lasted less than a week, before operations resumed as normal. The park, which opened in 2004, was financed and built by South Korean businesses (the South even provides the electricity) and in return, gives those firms access to more than 40,000 North Korean workers. It's just a few miles north of the Demilitarized Zone and is connected to the South by special rail and road access.