"The graveyards are full of indispensable men," growled Charles de Gaulle, but French history would have been very different if he had died in 1940 (no Free French government, probably a Communist takeover attempt when France was liberated in 1944) or even in 1960 (no quick exit from Algeria, no Fifth Republic). There are a few people whose absence would really make a difference.
Two such people seem to be hovering on the brink of death at the moment, though we have no trustworthy medical information about either one. In each case, their death could open the way to civil war. One is Thailand's King Bhumibol; the other is Venezuela's President Hugo Chavez.
King Bhumibol has spent most of the past two years in hospital, and few Thais expect him to live much longer (although this is never discussed in public). When he goes, the crown will probably pass to somebody who takes sides in the ongoing battle between "Red Shirts" and "Yellow Shirts" that has divided Thailand, and has already caused many deaths, over the past few years.
There was an election in Thailand yesterday. Opinion polls suggested that, as before, a majority of Thais would have voted for the party of former prime minister Thaksin Shinawatra, who was ousted by a military coup in 2006. About 90 Red Shirts, the mostly poor and rural supporters of Mr Thaksin, were massacred by the army in a confrontation in central Bangkok last year, and the army may try yet again to reject a pro-Thaksin election outcome.
Crown Prince Maha Vajiralongkorn was once close to Mr Thaksin and probably still secretly supports him, but he is a playboy who is neither loved nor respected by the public. His mother, Queen Sirikit, sympathises with the Yellow Shirts, and is rumoured to be angling for the army's support to make her regent when her (estranged) husband, King Bhumibol, dies, rather than letting the crown prince have the throne.
If the two royals were to align themselves publicly with the opposing sides in a struggle for the throne after King Bhumibol dies, they would substantially raise the probability that Thailand could stumble into a full-scale civil war.
Whereas if King Bhumibol can hang on for another year the dispute may be settled at the ballot boxes, with the army grudgingly accepting a restoration of the normal democratic order. He may not be utterly indispensable, but he is pretty important for Thailand right now.
And then there is Hugo Chavez. He is not exactly the "dictator" of Venezuela, as United States propaganda often calls him (he has been elected several times in free elections), but certainly he is a "strongman" in the classic Latin American style. He comes from the army, he once led an attempted coup, and he is a full-time demagogue. The only difference is that he is a strongman of the Left. And he may be dying.
Mr Chavez was in Cuba on 9 June, in a private meeting with Fidel Castro, when he suddenly fell ill. Cuban doctors were called in, and immediately operated on him for a pelvic abscess. But subsequent investigations showed that he had a cancerous tumour which also required surgery. He is currently undergoing chemotherapy, and the outcome is uncertain.
If Mr Chavez does recover, he might lose the 2012 presidential election anyway. He will have been in power for 14 years by then, and the mere passage of time has seriously eroded his power base. He has improved the lives of the poor, but a government with an oil income of bazillions of dollars that cannot even produce enough electricity to keep the lights on is bound to lose popularity.
Should Mr Chavez die now, however, there might not even be an election. His elder brother, Adan, the governor of the state of Barinas, reminded everybody "we cannot forget, as authentic revolutionaries, other methods of fighting". The army, whose senior ranks have been filled with Chavez loyalists, might back a "revolutionary" seizure of power.
On the whole, then, it would be better if Mr Chavez survived and came back to Venezuela, only to lose the election honestly next year. Like King Bhumibol, he is the indispensable man for the next little while.
• Gwynne Dyer is an independent London journalist.
