ZELEZNA, Czech Republic — The old schoolhouse stands alone at the end of a quiet country road flanked by snow-flecked wheat fields. From behind the locked door, opaque with smoked glass, come the clatter of sewing machines and, improbably, the babble of young female voices speaking Korean. The schoolhouse, which closed long ago for lack of students in this village of 200, is now a factory producing uniforms. Almost all the workers are North Korean, and the women initially looked delighted to see visitors. It gets lonely working out here, thousands of miles from home. They crowded around to chat....