The military has a key role in the country, and in particular in underpinning the authority of Kim Jong-il, son of "Great Leader" Kim Il-sung, who died in 1994.
But these are evidently not happy times for senior figures in North Korea. Given the lack of any reliable information from Pyongyang, it is hard to tell whether the cause is the winter, the worsening of the food situation, or something more sinister. South Korean media reported that Kim Kwang- Jin had been known to be ill for some time.
There has been a flurry of indications in the past few months that all is not well in North Korea. The prime minister was replaced ealier this year - ap- parently for health reasons. Chief ideologue Hwang Jang-yop, perhaps fearing a bout of dodgy health himself, defected to South Korea's mission in Peking, where he is still.
South Korean efforts to persuade China to allow Mr Hwang to travel to Seoul have so far yielded no progress; but South Korean officials believe he may be released as soon as next week. Once there, he will have to be on his guard. This week another North Korean defector died after being shot.
The defection showed that near-famine and economic ruin are combining with a power struggle to make North Korea a distinctly unhealthy place. All of these departures will accelerate change: they may be the product of Kim Jong-Il's desire to force the pace as he tightens his grip on power. He has not yet formally inherited the vacant titles of state president and general secretary of the Workers' Party.
Michael Breen, a Seoul-based consultant on North Korea, said that Kim, having used the old guard to secure his grip on power, has now found them blocking his tentative moves to take the country out of hostile isolation and establish dialogue with the United States. "One explanation of why things are moving so slowly in North Korea is because of problems retiring the old generation." he told Reuters news agency.
In South Korea, too, these are troubling times for the ruling party. President Kim Young-sam is attempting to restore his political image after a damaging financial scandal and a national confrontation over a planned new labour law.
Yesterday, he began by replacing his chief secretary and three other top advisers responsible for political, economic and general affairs. "This is the start of a major reshuffle in the government and the ruling party." a Presidential spokesman said. "The cabinet reshuffle is expected early next week."
The President promised on Tuesday to deal sternly with anybody - even close associates and family - who was involved with corruption, and began by banishing his son, Kim Hyun-chul. Yesterday a high-ranking government intelligence officer was also fired after he was accused of providing classified reports to the disgraced son.
The South Korean parliament is also considering a new version of the controversial law on trade unions, but it is unlikely to be finalised before the end of next week. Unhappy with the pace of legislation, the Korean Confederation of Trade Unions - which is outlawed and independent of the official trade unions - had called for a half-day strike yesterday, but the response was tepid.