SEOUL, South Korea — North Korea's newly minted leader presents the U.S. and its allies with a strategic challenge: how to deal with an inexperienced young man who sits on a nuclear arms program, a stash of chemical weapons and the world's fourth-largest army.

Kim Jong Un is poised to become the world's youngest commander in chief. With virtually no track record, he will be learning on the job. From a military perspective, that makes him a huge wild card.

While the transition could offer an opportunity for positive change, this week's announcement of North Korean leader Kim Jong Il's death immediately set off alarms in situation rooms from Seoul to Washington. Troops around the region are on heightened alert.