North Korea's fifth nuclear test showed "irrationality and recklessness," Lieutenant General Chun In-bum, who retired in July as Deputy Commander of South Korea's First Army, told NK News on Monday.

And that could soon pose a problem, because if Kim Jong Un miscalculates that "the democratic world is inept and unwilling to act," the North Korean leader could end up doing "something really stupid" that puts the Koreas in a situation that "both sides don't want."