The cold war has returned to the Korean peninsular. An international board of investigation has confirmed that North Korea was responsible for the unprovoked sinking in March of the Cheonan, a South Korean warship, with the loss of 46 sailors. This follows the revelation by Seoul last month of a North Korean plot to assassinate a high-profile defector.

Pyongyang has reverted to the tactics of the 1970s, when assassinations and cross-border sabotage were a standard tool of policy.

Quite why is less clear. There is some evidence that North Korea is facing a domestic crisis. A currency revaluation over the winter was botched, leading to food shortages. Greater aggression towards the South may also be part of a succession strategy by Kim Jong-il. The country's ruler, who suffered a stroke two years ago, is reportedly lining up his third son as his successor. It has even been suggested that the sinking may have been a maverick act – a power play by a renegade military commander within North Korea.