In earlier times, the the existence of "mutually assured destruction" ensured a kind of tense stability, with much sparring over contested zones. Only once - over Korea in the mid-century - did a serious and prolonged conflict between major powers break out. This was due to an ambiguous signal sent out from the United States, misinterpreted by Stalin as meaning that the US would not go to war over South Korea, so that his own protectorate of North Korea could invade South Korea with impunity.
This was an expensive lesson for both superpowers, and both soon developed more sophisticated techniques for the avoidance of direct conflict. Both superpowers made ingenious use of the United Nations for this end. Thus, in 1957, over the crisis in Hungary, President Eisenhower used the United Nations to get out of a trap which his own propaganda had constructed for him. For years the US Government had been promising to "roll back the Iron Curtain".
Unfortunately, this language was used in broadcasts to Eastern Europe, mainly through Radio Free Europe. The broadcasts were taken as implying that if any Eastern Europeans revolted against the Soviet Union, they would have military support from the United States. Believing this, Imre Nagy, Prime Minister of Hungary, decided to withdraw from the Warsaw Pact, thus presenting a direct challenge to the Soviet Union.
There thus emerged a serious risk of conflict between the US and the Soviet Union. Eisenhower saw that a war between the two superpowers in Central Europe would be a huge disaster, involving enormous casualties, including American casualties. But how to get out of the terrible trap constructed by his own past rhetoric?
Eisenhower decided to use the United Nations for this purpose. He claimed that the United States was bound by international obligations, specifically the Charter of the UN, not to intervene unilaterally and could only act through the United Nations. This was quite false. There is nothing in the Charter to prevent any power from acting unilaterally, or in concert with others, if it considers its vital interests are at stake. But to put the spotlight on the UN, and away from the United States, enabled Eisenhower, to pass the buck in a dignified manner.
So the matter came, in the first instance, before the Security Council. There, altogether predictably, the Soviet Union vetoed UN intervention. The matter then came before the General Assembly, where the United States at that time controlled a safe two-thirds of the vote. The United States welcomed the verdict of what it then still called "the moral conscience of mankind" represented by the General Assembly.
In the upshot, the Soviet Union got away with invading Hungary, and the United States got away with letting down the Hungarians.
After the disintegration of the Soviet Union, the United Nations lost the kind of relevance it had had while there were still two great powers. President Bush did make some use of the UN during the Gulf War, but it was mainly a way of lending some international dignity and decorum to the motley consortium of allies, brought together by Saddam Hussain's expansionist aggression.
The United States is now by far the greatest power on earth. But it was - and is - remarkably timorous and fragile for a power able to draw on such stupendous resources. At least twice it has been forced to back away in the face of aggression from almost ridiculously diminutive adversaries. Thus, Ronald Reagan backed out of Lebanon after a guerrilla gang, backed by Syria, had inflicted heavy casualties on a detachment of American marines. Similarly, Bill Clinton, having adopted an apparently militant position in Somalia, abruptly backed away after smaller casualties had been inflicted on American forces there. By now, even very small countries facing potential conflicts with the Americans know that the worst they have to fear is aerial bombardment, as in this week's attacks on Afghanistan and Sudan. Ground forces will probably not be sent in at all and, if sent in, will be withdrawn at the first sign of serious trouble.
Not only does this condition give relatively small countries with aggressive propensities - such as Iran, Iraq and Syria - unprecedented freedom of action. It also encourages paramilitary groups, even quite tiny ones, in the belief that they can make progress towards their objectives by a judicious mixture of violence, threats and political negotiation. Not only does the United States respond in a promising manner - from the point of view of the terrorists - but other powers do also, including Britain.
The terrorist group which has made the most skilful use of this situation is - not surprisingly - the oldest terrorist group in continuous existence: the IRA, with its seasoned and resourceful political arm, Sinn Fein.
What is going on, within the present British Government in relation to Sinn Fein-IRA, is in many ways, but not in all, closely similar to what went on within the government of Neville Chamberlain from 1936 to 1939 in relation to Adolf Hitler. What was going on under Chamberlain has gone down in history as "appeasement". Today, in relation to Sinn Fein-IRA, appeasement passes under the even more euphemistic name of "the peace process".
In both cases, a party threatening violence was rewarded. But, in the case of Chamberlain and Hitler, the appeasement of the potential aggressor was much more understandable - if not defensible - than is now the case in relation to Sin Fein-IRA. What Chamberlain was trying to avert, however forlornly, was the risk of a war with what had then become the world's greatest military power. The present British Government - and the Irish Government also - are almost frantically seeking to appease a motley collection of a few hundred terrorists.
Appeasement was not a success in the Thirties, and is not a success now, in its present "peace process" garb. The "success" of the peace process in the Good Friday Agreement was almost frantically celebrated at the time in a torrent of media guff about the supposed advent of peace on earth. The guff ignored among other obvious realities the fact that while Sinn Fein, the political wing controlling no weapons at all, endorsed the peace agreement, the IRA, in control of all the weaponry, quietly indicated that while it had no objection to whatever Sinn Fein might choose to sign up to, it did not regard Sinn Fein's signature as in any way binding on the IRA.
Last week's bombing at Omagh was the most destructive act of terrorist violence since the foundation of the Irish Free State 77 years ago. Formally, the Omagh bombing was not the work of the Provisionals but of a "breakaway" group calling itself "the Real IRA". But such "breakaways" are too convenient to be accepted at face-value. It is doubtful whether any terrorist attack could be planned and carried out in a place like Omagh without some collusion on the part of the local Provisionals. Both the personnel and the weapons involved derive from the IRA, and the event is in line with the IRA's purposes and procedures.
While the IRA's own ceasefire holds, Sinn Fein, acting for the IRA, enjoys widespread international approval and uneasy respect. That is precisely the combination - with an emphasis on the "uneasy" - that it has hoped to achieve. After Omagh, for which, incredibly, almost nobody accords it any degree of blame, this combination is enhanced. Sinn Fein, with the Provisional IRA along right behind it, fully armed, is seen as acting "responsibly", unlike the vile murderers calling themselves "the Real IRA". And when the peace talks resume in the autumn, Sinn Fein will expect to be rewarded for good behaviour. On past form, it will receive its rewards in such shapes as the "reform" of the RUC, to the specifications of the people who have murdered nearly 300 members of that force, over the past 25 years.
This month saw, I believe, the worst terrorist outrages since the Second World War. The bomb toll at Omagh was the worst in these islands over that period. The bombings of the US Embassies in Nairobi and Tanzania, which killed a total of 257 people, mainly in Nairobi, were the worst in the world.
What hope is there of combating terrorism effectively? As far as the Arab and Muslim countries principally affected are concerned, I can see little immediate hope. There are a large number of terrorist organisations involved, with covert backing from several Arab or Muslim countries, the most active and ingenious being Syria. There is widespread public support in these countries for terrorist activities, especially when directed against Israeli or American targets. In addition, there are many religious fanatics who believe that persons who die in the course of attacks on infidels will go immediately to Paradise.
In the circumstances, American efforts to combat terrorism can easily become counter-productive. Americans cannot rely on local people to combat terrorism, with which these people are usually in at least some degree of covert sympathy. At present, Americans are going in there, in response to the pressures of public opinion at home, and trying to do the job for themselves. But they are singularly ill-equipped to do this. They generally do not understand either the language or the culture with which they have to deal. Those sent there on these missions are likely to become targets of those whom they were sent to expose and defeat. And, when they do become targets, Americans are likely to withdraw from the areas precipitately, as before, leaving the terrorists more entrenched than ever.
It would be better to withdraw from the affected areas as soon as possible, and in as good order. The countries involved could then be isolated, in terms of trade and aid, and informed that these will only be restored if the countries concerned deal adequately with the terrorist organisations they have been harbouring. There is no guarantee that this approach would work, but nothing more promising appears to be on offer.
Middle Eastern terrorism will be a hard nut to crack, if ever it is cracked. Other kinds of terrorism would be a lot easier to crack, if governments only can find the will to clamp down on them effectively. Irish terrorism is a case in point. Most Irish people, North and South, do not approve of terrorism, but are afraid of terrorists. The terrorists are few in number, and the most experienced are well known to the police. They cannot be dealt with effectively in the course of normal policing, and judicial process, mainly because witnesses are understandably afraid to come forward.
In the circumstances, this means that terrorism cannot be combated without the resolute and impartial application of internment. A myth has been allowed to establish itself, according to which "internment has been tried and failed" and proponents of this myth were heard from again this week. Internment has been tried on three occasions in Ireland since the start of the Second World War. It was used successfully against the IRA by Eamon de Valera during that war, when the IRA regarded themselves as allies of Nazi Germany, and this threatened de Valera's policy of Irish neutrality. It was used, again successfully, by Sean Lemass in the late Sixties, when the IRA attempted to wage "war" on Northern Ireland from bases in the Republic.
There are some signs this week, after Omagh, that things may at last be moving in that benign direction. The Dublin Government has just introduced a package of measures - stopping just short of internment - which are tough enough to win the approval of Ulster Unionist leaders. We are now told by both Governments - for the first time in 20 years - that internment is "not ruled out".
The terrorists have not given up, but the next group of them to practise or resume violence seems likely to have to face internment. And then we shall see.
Conor Cruise O'Brien's autobiography "Memoir: My Life And Themes" will be published in October