Five years since the conflict in Darfur began, BBC News website's World Affairs correspondent Paul Reynolds asks why international concern has not been translated into effective intervention.
The deep concern about Darfur felt internationally has not been matched by a similar determination to intervene.
The peacekeeping force in Darfur has been weak
It is not from lack of knowledge.
There have been many reports, from the UN and others, which have laid the blame largely at the door of the government of Sudan.
The US has called the killings genocide, though the UN held back from using that word.
However, whatever it is called, no major power was willing to send its own forces to try to put an end to it.
Instead, diplomacy has centred on putting pressure on the Sudanese government to restrain its armed forces and the Janjaweed militias it is accused of supporting - charges it denies.
Sudan has also been pressured into allowing in peacekeeping forces, first from the African Union (AU) and then from a mixed AU-UN force including other international troops.
However, those peacekeepers have been weak. The African Union force has been ineffective. The wider international force has not been properly deployed.
Diplomacy not enough
A great deal of effort has also been put into trying to solve the underlying political problems which led to the first rebel attacks in 2003, but these talks, amounting to agreements sometimes, have a habit of fading away.
The best aspect of the world's response perhaps has been humanitarian. Undoubtedly many lives have been saved.
One of the problems for the outside world is that it has been dealing with a very determined government unwilling to concede much in what it sees as a major threat on its own territory.
More than two million have been displaced by the Darfur conflict
Another is that the rebel groups have not been united and have not always been ready to make a peace agreement.
Clearly, diplomacy has not been enough.
"The Americans were quite driven over Darfur, but were hamstrung by their great achievement of the North-South agreement in Sudan," says Richard Dowden, executive director of the Royal African Society in London.
"This meant they could not apply too much pressure on Khartoum over Darfur because its co-operation was needed for the North-South implementation.
"Sudan was able to manipulate African opinion and blunt whatever pressure there was.
China, which buys about 60% of Sudan's oil and sells it weapons, has also played a key role in helping Sudan avoid UN sanctions.
"Although China did in the end persuade it to accept the hybrid force, breaking its own rules about not intervening in the political affairs of the countries in which it invests," Mr Dowden notes.
"If the US had not done Iraq, it might have done Darfur, but the mood in the West was that this was an African problem and an African solution should be sought.
"If there was genocide, then it happened in 2003/4. By the time the world got round to acting, it was too late."
Mention of Iraq raises the issue, though, of whether any intervention in Darfur would have produced its own problems, given the opposition of the Sudanese government.
One example of how interested the world is in Darfur but how powerless it has been can be seen in the role of the International Criminal Court.
The court has indicted (but has not managed to have arrested) two Sudanese officials for war crimes - Ahmad Harun, currently the minister for humanitarian affairs, and Ali Kushayb, leader of the pro-government Janjaweed militia.
In a statement in February 2007, the court's prosecutor described how the "turning point" in the conflict was the rebel attack on Fasher airport in North Darfur in April 2003.
Ahmad Harun, the prosecutor said, was then appointed interior minister.
"Shortly after Harun's appointment, the recruitment of militia/Janjaweed greatly increased, ultimately into the tens of thousands.
"The vast majority of attacks in Darfur were carried out by the militia/Janjaweed and the armed forces... they targeted civilian residents based on the rationale that they were supporters of the rebel forces.
"This strategy became the justification for the mass murder, summary execution, and mass rape of civilians who were known not to be participants in any armed conflict. The strategy included the forced displacement of entire villages and communities."
Yet Ahmad Harun nor Ali Kushayb have not been arrested and handed over by the government of Sudan.
Indeed, Ahmad Harun was subsequently put in charge of government refugee camps and has been appointed to the group monitoring the deployment of the AU-UN force.
In December 2007, ICC prosecutor Luis Moreno-Ocampo told the Security Council:
The international humanitarian response has saved many lives
"In Darfur in 2003 - 2004, we witnessed the first phase of the criminal plan co-ordinated by Ahmad Harun. Millions of people were forced out of their villages and into camps.
"In the second phase - happening right now in front of our eyes - Ahmad Harun is controlling the victims inside the camps... women are raped... the displaced are surrounded by hostile forces; their land and homes are being occupied by new settlers. The rationale is the same as before: target civilians who could be rebel supporters.
"As long as Harun remains free in Khartoum, there will be no comprehensive solution in Darfur."
Such talk shows how much has yet to be done.