After the Cold War confrontation, with its potential for a war more "absolute" in its destructiveness than any that had preceded it, we have returned to a situation that in some ways resembles the later colonial period, and in others the 18th century. However, the growing role of the media in shaping international public opinion and the presence of an international authority to oversee the rule of law between states - the United Nations - has made a difference.
The clear distinction between "war" and "peace" - a product of nearly 200 years in which wars got bigger and involved more and more of society - has been blurred again, as we contemplate continuous engagement in other peoples' wars.
In the early 19th century, Karl von Clausewitz, the military strategist, wrote that his era was seeing the end of "cabinet wars", 18th-century wars fought by small, professional, mercenary armies for limited objectives. "War was handed back to the [mass of the] people from whom it had been taken away, in part, by the use of select, standing armies."
Now it has been taken away again, as we fight highly political wars for precise objectives. Even the countries that have the longest traditions of mass conscript armies - France and Russia - have recently returned, or shown signs of returning, to an 18th-century model with small professional armies to fight small, professional wars.
The idea that we should intervene in other people's wars - civil wars - to enforce international standards of behaviour takes us back even further. Back beyond 1648, when the delegates at the Peace of Westphalia ended the terrible international and religious Thirty Years' War, which had raged across the whole of Europe. They then agreed a principle which lasted almost 350 years - that what happens within a nation state is that state's business and nobody else's . Diplomacy, war and peace were conducted on that principle. There were civil wars, but "real' wars took place between nations.
No longer. The latest yearbook from the Stockholm International Peace Research Institute confirms that the 30-odd "major armed conflicts" under way last year were all internal, civil wars. Yet the armed forces of Britain and France, to name only two major powers, have never been busier.
The implications are profoundly uncomfortable. In the end, we may have to ditch some of our most cherished preconceptions.
We are not now at war. We were not at "war" in the Falklands, either, nor were we at "war" in the Gulf. Yet now we have 18,500 British soldiers in Northern Ireland and 11,000 in Bosnia - a quarter of Britain's "peacetime" army on active service. There are another 30,000 ready to take over every six months, so in the course of a year, half the army at least is called into action for real. We are clearly not at peace, either. As this newspaper suggested last month, we may be seeing the end of "war" and "peace".
We are certainly living through the biggest revolution in strategic thought since at least the time of Karl von Clausewitz (1780-1831).
Most educated people have heard of Clausewitz, but few have read him. His picture comes as a surprise: a sensitive, youthful face, like the writer and philosopher he was, beneath a slightly eccentric, romantic explosion of curly hair.
This was the man whom Basil Liddell Hart, one of Britain's leading military theorists this century, described, wrongly, as "the Mahdi of mass and mutual massacre". Nothing could be further from the truth. In the horrors he witnessed during the Napoleonic wars, Clausewitz saw warfare slipping from the leash of political restraints, striving to follow its own logic and threatening to pervert the political objectives for which it was waged.
Clausewitz, who insisted war must remain a tool of politics, was issuing a warning. But subsequent generations blamed him for the slide into "total war" that followed. It was not only a question of 19th-century developments in technology, but of social organisation, as states were able to impose their will on the populace to a greater extent.
"Total war" was waged by the Union at the end of the American Civil War, and reached its full extent in the First and Second World wars. Every aspect of national life was directed towards the war effort. The political objectives for which the wars were started were forgotten as total victory became the only goal.
Then came nuclear weapons. As Professor Richard Overy has argued, they made war more absolute - in the sense that it became possible to annihilate the human race. But they did not necessarily make it more total - in the sense of the First and Second World wars. Far from mobilising the entire resources of the nation to fight in various ways, most of the population, in planning for nuclear war, was written off.
Right through the 1980s, the two great military blocs prepared for Armageddon while realising that in such circumstances, war, as a tool of any rational politics, made no sense. Then came the end of the Cold War, in 1989, and the break-up of the Communist empires, coinciding with the Gulf war.
The result has been utterly dramatic. Like the revolutions in science analysed by Thomas Kuhn, revolutions in warfare embody all the characteristics of paradigm shift.
A paradigm, Kuhn explained, is a whole package of assumptions, procedures and practices that together make up the way the scientific community - in this case, strategists - go about their business. Many of the changes have been around for a while. But suddenly they all coalesce, and there is a revolution. They are often associated with one individual: Copernicus in astronomy, Newton and Einstein in physics, for example. But in fact they embody many ideas that have been circling on the sidelines for years.
So with our new paradigm. In the shadow of total war, smaller, though often still significant wars continued, partly because full-scale conflict between the nuclear-armed powers was too dangerous, and partly because the vast investment necessary to prepare for full-scale nuclear war left nations vulnerable to alternative approaches.
Seventies theories of guerrilla warfare, and what used to be called "low- intensity operations", all have some relevance to the new world order. But so too do the sophisticated military technologies and tactics developed for the Third World War. Many of them, including the US Air Land Battle doctrine and precision-guided munitions - proved ideal for smaller wars where avoiding casualties - your own and the enemy's - was crucial. The l991 Gulf war and the operations against the Bosnian Serbs in summer 1995 are the prime examples.
But alongside all this, which pointed to a return to small, professional, highly disciplined 18th-century armies, manoeuvring with precision and often used in support of civil authority, our new paradigm has another element. As the UN Secretary General, Boutros Boutros-Ghali, wrote in 1992: "The centuries-old doctrine of absolute and exclusive sovereignty no longer stands, and was never so absolute as it was conceived to be in theory",
The previous year, just after the decision to intervene to help the Iraqi Kurds, against the will of the Iraqi governments, Xavier Perez de Cuellar wrote something similar. "We are witnessing what is probably an irresistible shift in public attitudes towards the belief that the defence of the oppressed in the name of morality should prevail over frontiers and legal documents."
This was not merely pre-Clausewitz. This was going back before the Peace of Westphalia, to an era when wars were fought on grounds of international morality and theology. Some 20,000 troops were moving into northern Iraq without the consent of the Iraqi government, not in defence of any vital western interest, as the recapture of Kuwait had been, but in defence of the oppressed.
This phenomenon is perhaps the most extraordinary part of the paradigm. Strategic thinkers now recognise we no longer just fight "wars of necessity" - wars where our immediate vital national interests are affected. We fight "wars of choice" including, in some cases "wars of conscience".
These wars of conscience are clearly driven by moral outrage, often fanned by the media. But they are also a result of changes in the international scene. We live in a global society. Many would argue that there is no direct British national interest involved in Bosnia, never mind the more distant mountain forests of Rwanda and Burundi. But if you belong to a global society, and have a seat at the top table of the world governing body, you cannot separate your vital interests from your responsibilities to the world community. That appears to be the attitude of the present Conservative government, and also of a future Labour government. You do what you do well. You punch above your weight.
The change in attitude can be plotted fairly precisely, to just after the Gulf war. The operation to protect and feed the Kurdish refugees in Iraq in April 1991 was the first example of an international military operation of this type, apart from the Congo in 1960-64. A UN force under the command of the UN Secretary-General, complete with its own air force, was initially committed to a peace-keeping task, which later switched to "peace enforcement". It was a unique, remarkable foretaste of what was to follow three decades later. However, all the new-style interventions in other peoples' wars have taken place in what are called "weak" or "failed" states. The international community was prepared to intervene in Iraq, broken by the Gulf war. It was prepared to intervene in Bosnia after the Bosnian government proved incapable of withstanding attack by the rebel Serbs. The international community is still not ready to intervene in big, powerful well-organised states. Northern Ireland is one example. Chechnya is another. The slaughter and atrocities in Chechnya and the media coverage they received - would have initiated massive intervention had they not taken place in Russia. When the nuclear-armed superpower lashed out with its steel-shod paw, there was much muttering. But this was not a puppy to be scolded. This was a bear. They left him alone.
Half a century after the UN Charter was written, it remains unchanged. It was written in the aftermath of the Second World War, when the "United Nations" were, in fact, the victorious powers. It concentrates overwhelmingly on international peace and security. It contains nothing about traditional peace-keeping - the UN's most successful, if accidental, stock-in-trade. And certainly nothing about the whole new spectrum of intervention operations that has opened up between traditional peace-keeping and war. When the UN was created, many envisaged it would have its own armed forces, able to intervene swiftly, untrammelled by national interests and domestic political concerns, Instead, it trawls around for forces, which usually arrive, as in Bosnia and Rwanda, too late. The same may happen in Burundi. The end of "war" and "peace" is a global issue, and requires a global response.
Christopher Bellamy is defence correspondent of the 'Independent' and has reported from the Gulf war, Bosnia and Chechnya. His new book, 'Knights in White Armour - the New Art of War and Peace', is published on Thursday by Hutchinson, pounds 17.99.Reuse content