The North Korean threat

A South Korean soldier mans a checkpoint in Paju, South Korea.  (Chung Sung-Jun / Getty Images)

The U.N. Security Council, meeting in March, votes for tough new sanctions against North Korea in response to its latest nuclear test. An angry North Korea responded with new threats.  (Bebeto Matthews / Associated Press)

Soldiers patrol a fence near Dorasan in Paju, South Korea.  (Chung Sung-Jun / Getty Images)

South Korean soldiers in Pocheon take part in training in case of an attack by North Korea.  (Ahn Young-joon / Associated Press)

U.S. Army vehicles take part in joint drills with South Korea in Yeoncheon, near the border with North Korea, which called the routine annual exercises preparation for an invasion.  (Ahn Young-joon / Associated Press)

South Koreans return with their belongings from the Kaesong, North Korea, industrial park run by the rival Koreas. North Korea pulled its workers from the complex, effectively halting activities there.  (Lee Jin-man / Associated Press)

South Korean vehicles return home from North Korea’s Kaesong industrial park after the North pulled its workers from the complex.  (Lee Jin-man / Associated Press)

South Korea moves tanks across a temporary bridge during an exercise near the border with North Korea.  (Kim Jae-Hwan / AFP/Getty Images)

South Korean Marine K-55 self-propelled howitzers take part in a military exercise near the border village of Panmunjom.  (Ahn Young-joon / Associated Press)

Smoke bombs explode near South Korean tanks during an exercise near the demilitarized zone in Hwacheon, South Korea.  (Lee Hae-ryong / Associated Press)