Yes, a full-scale military invasion would meet with a devastating defeat by superior South Korean and US military forces, whose current naval exercises in the Yellow Sea are designed to remind North Korea of this disparity. But, with 15,000 artillery tubes embedded in the Demilitarized Zone, just 30 miles north of Seoul, North Korea knows that firing just a few shells could wreak havoc on the South Korean stock market and economy, while it has less to lose in comparison.