How does power pass from father to son in North Korea?

In North Korea, power passes within one family, from Kim Il Sung to his son Kim Jong Il to his grandson Kim Jong Un, and each handover was prepared for years. The state's founder chose his son early and the party then confirmed it, which is how the Kim dynasty was established.

Kim Il Sung's oldest son, Kim Jong Il, was his designated successor as early as 1974. He was elected to the party's Presidium at the 6th Workers' Party Congress in 1980, named commander-in-chief in 1991, and became Supreme Leader when his father died in 1994. He took over in a catastrophic economic crisis after the Soviet Union dissolved, which brought a famine, and he strengthened the role of the military with his Songun, or military-first, policies.

The next handover was prepared more quietly. From 2009, Kim Jong Un, the youngest son, was viewed as the successor. On 27 September 2010 he was made a four-star general despite no previous military experience, the first time North Korean media mentioned him by name. For many years only one confirmed photograph of him was known outside North Korea, apparently taken in the mid-1990s when he was eleven.

When Kim Jong Il died, the government announced it on 19 December 2011, two days after the death, and state media hailed Kim Jong Un as the Great Successor. Two violent breaks with relatives followed: his uncle Jang Song Thaek was arrested and executed in December 2013, and his exiled half-brother Kim Jong-nam was killed in 2017, an act Kim Jong Un is widely believed to have ordered.