Intervention in the affairs of another state can be justified, as long as the threshold is high and the commitment is there for the long run.

Few things irritate me more than reading headlines criticising the United Nations, saying the UN should act to stop violence, prevent civil war and solve some humanitarian crisis. The world watched with horror the genocide in Rwanda, what was Yugoslavia, Iraq a few years ago, and now the horrors of Sudan. The UN gets the blame when nothing happens. Yet the UN can only do what its members allow, fund and mandate it to do.

Correctly, it has no army, it cannot force its way in. Frequently leaders call for action and then will not fund or equip the UN to do the job. Or the politics of the Security Council and the veto stops direct action. Or a weak mandate puts peacekeepers in an impossible situation where they sit by powerless to enforce a peace.

Massacres, the most appalling acts of barbarism, have been committed under the noses of lightly armed blue-helmeted UN soldiers who are instructed not to use force.

The first contingent of blue helmets was based in the Sinai after the Suez crisis where the British, French and Israelis conspired to create a situation to legitimise an invasion after President Gamal Abdel Nasser of Egypt nationalised the Suez Canal. Later, when Arab nations attacked to reclaim land lost in the war, the UN troops were asked to stand aside. They did. They had to.

That has been, sadly, a common experience. Bluntly, what normally happens is that the North Atlantic Treaty Organisation in the Balkans, Britain or France in Africa, move in to forcibly create a peace or a stand-off, and then the UN is mandated to maintain the peace. Peacekeeping is different to peacemaking. There has to be a peace to keep.

Take present-day Afghanistan. It's heartbreaking and breathtaking in its cynicism the way in which governments call for action and then deny the UN and a desperate, vulnerable new government the resources to rebuild and construct their nation.

For centuries the principle of governments having the right to conduct their own affairs without outside involvement has been at the centre of international relations. But does this mean sovereignty allows the dominant political force to maim, torture and commit genocide?

Article 51 of the UN charter only sanctions force in self-defence or when approved by the Security Council to stop an act of aggression. Intervention is illegal in matters which are essentially within the jurisdiction of any state. That's the legal premise that Sudan has used to warn countries not to intervene in its domestic affairs. However, there is a 1948 UN convention on genocide which can give states the legal authority to take measures or can be used to enlist UN action where genocide is established.

Despite visits by UN Secretary-General Kofi Annan, condemnation by US Secretary of State Colin Powell and numerous world leaders of the tragedy that is Sudan, the UN resolution only calls for sanctions, not intervention.

Annan has been urging nations to assist with funds for what has been called the greatest humanitarian crisis in the world, in western Sudan. At the same time, Sudanese President Omar el-Bashir was in the European rogue state of Belarus buying weapons to continue the genocide in Darfur.

President Aleksandr Lukashenko of Belarus cheerfully ignored UN sanctions and sold weapons to Saddam Hussein during the embargo, and is now reported to have sold weapons to six of the seven nations on the US State Department's list of state sponsors of terrorism. Yet he goes unpunished.

The Sudanese government claims it cannot disarm the Janjaweed militia it created and claims immunity from an enforced solution in the name of sovereignty.

At the moment of writing, only the French have troops on the ground and that's in neighbouring Chad to protect the thousands of refugees who have fled. Khartoum has rejected the African Union's offer of troops.

The Security Council gave Sudan 30 days to answer genocide accusations. A lot of people will die within that timeframe. One interesting factor for those who believe in international law and order is the Sudan government's fear of prosecution for crimes against humanity in the International Court in The Hague. Knowing there could be a process of international justice against murderous leaders can change behaviour.

A new theory of international engagement is emerging that brings this dilemma and these contradictions into sharp focus. The age-old theory of sovereignty, the right to self-determination, the right to non-intervention, just won't do any more. The new doctrine is a "right" and "obligation", the responsibility to protect.

The threshold for direct action must be very, very high. First, it must be do-able. Diplomacy must be given every chance and then some. Action must be followed through with resources and a plan for stability. Military planners talk of an exit strategy. Equal to this must be the plan for reconstruction.

As we have learnt from Iraq and elsewhere, winning the war can be the easy part. Winning the peace is a long, expensive and dangerous process.