The ruler of North Korea, Kim Jong-il, passed away on Saturday.

He died, at age 69, of heart failure.

North Korea’s people know him as “Dear Leader.” They went into the streets to mourn his passing.

However, his death creates a lot of uncertainty about what will happen in North Korea.

Many world leaders are concerned about the situation there now.

One reason is that North Korea has nuclear weapons, so nearby countries like Japan and in particular South Korea, reportedly have their military on “high alert.”

Another reason for concern is that before his death, Kim passed control of the country to one of his sons, Kim Jong-un, who is in his 20s.

Kim Jong-un is largely unknown to other world leaders. In fact, until two years ago, the only picture the CIA had of him was as a student in short pants at a school he was attending in Switzerland.