Regime tests the limits of a MAD world If there is a state that might defy the logic of nuclear deterrence, it is North Korea The thing about MAD is that it requires both sides to be sane. Ever since the onset of the nuclear age, the doctrine of mutually assured destruction, or MAD, has kept the peace. The calculation that, ultimately, no rational political leadership would risk millions of deaths in their own nation has seen the world through some perilous moments - from the Cuba missile crisis to the fall of the Berlin Wall. The most alarming aspect of the current crisis with a nuclear-armed North Korea is that the regime there might be one of those rare abberations, to which the normal logic of nuclear deterrence does not apply. Gideon Rachman Every now and then, during the cold war, there was a suggestion that some political leader might be prepared to think about the supposedly unthinkable. In the late 1950s, Mao Zedong shocked even the hard-bitten former Stalinists of the Soviet Union when, on a trip to Moscow, he suggested that nuclear war might not be so bad after all, telling his startled hosts: "If the worst came to the worst and half of mankind died, the other half would remain. Imperialism would be destroyed, and the whole world would become socialist. In many respects, North Korea has replicated some of the very worst features of Maoist China: the isolation from the outside world, the labour camps, the cult of personality and the willingness to tolerate mass starvation at home. The latter is particularly chilling, when one remembers that nuclear deterrence is meant to rely on an unwillingness to accept the death of millions of your compatriots. There is still an unfortunate tendency in the west to treat North Korea as a bit of a joke. The internet is full of "hilarious" photo-shopped pictures of the podgy young leader of North Korea, Kim Jong-eun. In reality, the Pyongyang regime is about as unfunny as it gets. It is a totalitarian nightmare that has ruined the lives of millions of people - and that now openly threatens the outside world with nuclear weapons. Trying to guess what the North Koreans are really thinking is a difficult, but crucial, task. At times, there have been suggestions that the leadership may understand the outside world better than is sometimes supposed. I once asked a senior Chinese diplomat who had frequent dealings with Kim Jong-il, the father of the current leader, whether the North Korean dictator had any real knowledge of the west. "Of course," came the reply, "he spends all night on the internet." There was some hope that his son would open an even wider window to the outside world. Surely his time at a Swiss finishing school must have had some impact? At present, however, the younger Kim is taking North Korean nuclear posturing to new and even more dangerous levels. In recent days his government has said that it is now in a state of war with South Korea and has talked of launching nuclear strikes on the US. The American and South Korean response has been taken from the classic MAD playbook. By sending nuclear-capable bombers on a trial run over South Korea, the Americans are responding as the theorists of nuclear deterrence would advise: "Don't blink. Don't show weakness. The other side will back off, rather than risk nuclear annihilation. Seoul has also said that its military should respond immediately to any provocation, without considering the wider political implications. The danger is that such policies assume a rational adversary. Indeed America's foremost experts on North Korea, such as former ambassador Chris Hill, continue to argue that North Korea has no real intention of provoking a conflict with the US. The real danger, they say, is that an inexperienced leadership in Pyongyang will provoke a conflict by accident. Even then, the assumption is that any exchange of fire is likely to be brief - and to stop well short of anything involving nukes. That is probably right. But the unsettling reality is that we cannot be sure. If there is a regime anywhere that might just defy the normal logic of nuclear deterrence, it is North Korea. That suggests that the current US and South Korean policy - based on unblinking firmness and a refusal to yield to "nuclear blackmail" - may need to be dialled down. The most important task now is to concentrate on calming the immediate situation. That may require fewer, rather than more, military exercises between the US and South Korea. In the long run, the best hope for peace on the Korean peninsula must be internal change in the North. For beneath the surface, North Korea is changing. There is now far more trade with the outside world than there was a decade ago. Since 2005 the two Koreas have run a joint industrial zone inside the North that employs more than 50,000 North Koreans, working for companies from the South. Small commerce across the Chinese border has boomed, and the space for personal wealth and freedom has expanded a little, as goods and news from the outside world have penetrated the country. Given these economic shifts, China's current emphasis on the need for trade and dialogue with North Korea may be something more than the feeble evasion that is often portrayed in the west. If the North Korean leadership can be talked out of its nuclear bunker - and encouraged to engage commercially with the outside world - the prospects for peaceful change will be hugely enhanced.