While we don't ultimately know what prompted North Korea's nuclear test, we do know that Kim Jong-Il was hospitalized last fall, and that he is maneuvering to appoint a successor. Last September, TNR reviewed Kim's options:

Of Mr. Kim's four children from three mothers, his youngest son, Kim Jong-un, is thought to be his favorite, but being only 24 and third in line, it would seem very difficult to jump two sons in the succession. In a society organized along patriarchal lines, his daughter is not considered in the running.

Of the first two sons, it is the second son, Kim Jong-chol, 27, that many expect to have an edge in contesting the throne. We know this because he has occupied the same position in the propaganda department that Kim Jong-il did when he was young; because lapel pins bearing his likeness have been making their way around the country; and because his mother, a famous North Korean dancer, has transformed into something of a national icon. Still, Kim apparently has mixed feelings about his second son. At least according to his former sushi chef, the dictator finds his son to be "too much like a girl." Klingner, the North Korea expert, said certain reports had referred to Kim Jong-chol's hormone problem, which may or may not have led him to have developed breasts.

The oldest son, Kim Jong-nam, 37, is also a strong contender. He has had several key leadership positions in the North Korean secret police and army, but has fallen in and out of favor with the dictator. He reportedly soured his relationship with his father when he was arrested, in 2001, for carrying a false Dominican Republic passport in Japan, an historical enemy of North Korea's. (He was purportedly there to visit Tokyo Disneyland.) There is also the possibility of Kim Jong-il's brother-in-law, Chang Sung-taek, 62, coming to power, though this would likely be as head of a collective leadership involving other prominent members of Kim's inner circle.

South Korean news subsequently reported that Kim Jong-un's was appointed to the National Defense Commission, a move that implies he is Kim Jong-Il's most likely successor. FP has more on Jong-un:

According to Kim Jong Il's former personal chef, Kim Jong-un was born in 1983 or 1984 to Kim's third wife, Ko Hyong-hui, and is allegedly his father's favorite son. Unlike his brother Kim Jong-chol, Kim Jong-un has a more forthright character and, some sources say, has exhibited leadership skills. He is rumored to have studied at the International School of Berne in Guemligen, Switzerland. Upon returning to North Korea sometime after 2000, his studies continued, most likely at Kim Il Sung Military University. There are varying reports that he speaks German, French, and English.

Kim Jong-un's career background has been just as opaque. In 2004, reports began to surface that he and brother Kim Jong-chol were accompanying their father on inspections of military installations. In 2007, a flurry of reports emerged placing the third son in either the Korean Workers' Party's (KWP's) powerful Organization Guidance Department, where Kim Jong Il began his career in 1964, or the Korean People's Army's influential General Political Bureau. Both of these bodies are charged with surveillance and monitoring of the regime's powerful party, military, and security bodies.

There are also reports that Kim Jong-un may share some of the ailments of his father, such as diabetes, and might have been in a car accident last year. Therefore, his health is in question.

--Barron YoungSmith