PREDICTIONS of a world without food kept people awake a century ago. Half a century later, the nightmare du jour was global thermonuclear war - a spectre created by the US's detonation of a hydrogen bomb in 1952, and the Soviet Union's test the next year.

Soon, both superpowers possessed weapons a thousand times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki, and both were claiming the ideological high ground. The threat of thermonuclear war loomed like a vast, dark mushroom cloud.

Merely acknowledging this threat provoked widespread fear and loathing. Those who actually stared at the problem for any length of time risked insanity. And in the early 1960s, many believed there was no clearer proof of this than mad, bad Herman Kahn.

As an analyst at the RAND Corporation, a California-based think tank backed by the US air force, Kahn had spent years thinking what ...