The UN estimates that 3 million to 4 million Congolese have been killed, compared with the estimated 200,000 civilian deaths in Darfur. A peace deal agreed in December 2002 has never been adhered to, and atrocities have been particularly well documented in the province of Kivu - carried out by paramilitary organisations with strong governmental links. In the last month alone, thousands of civilians have been killed in heavy fighting between rebel and government forces vying for control of an area north of Goma, and the UN reckons that another 50,000 have been made refugees.

How curious, then, that so much more attention has been focused on Darfur than Congo. There are no pressure groups of any note that draw attention to the Congolese situation. In the media there is barely a word. The politicians are silent. Yet if ever there were a case for the outside world to intervene on humanitarian grounds alone - "liberal interventionism" - then surely this is it.

The key difference between the two situations lies in the racial and ethnic composition of the perceived victims and perpetrators. In Congo, black Africans are killing other black Africans in a way that is difficult for outsiders to identify with. The turmoil there can in that sense be regarded as a narrowly African affair.

In Darfur the fighting is portrayed as a war between black Africans, rightly or wrongly regarded as the victims, and "Arabs", widely regarded as the perpetrators of the killings. In practice these neat racial categories are highly indistinct, but it is through such a prism that the conflict is generally viewed.

It is not hard to imagine why some in the west have found this perception so alluring, for there are numerous people who want to portray "the Arabs" in these terms. In the United States and elsewhere those who have spearheaded the case for foreign intervention in Darfur are largely the people who regard the Arabs as the root cause of the Israel-Palestine dispute. From this viewpoint, the events in Darfur form just one part of a much wider picture of Arab malice and cruelty.

Nor is it any coincidence that the moral frenzy about intervention in Sudan has coincided with the growing military debacle in Iraq - for as allied casualties in Iraq have mounted, so has indignation about the situation in Darfur. It is always easier for a losing side to demonise an enemy than to blame itself for a glaring military defeat, and the Darfur situation therefore offers some people a certain sense of catharsis.

Humanitarian concern among policymakers in Washington is ultimately self-interested. The United States is willing to impose new sanctions on the Sudan government if the latter refuses to accept a United Nations peacekeeping force, but it is no coincidence that Sudan, unlike Congo, has oil - lots of it - and strong links with China, a country the US regards as a strategic rival in the struggle for Africa's natural resources; only last week Amnesty International reported that Beijing has illicitly supplied Khartoum with large quantities of arms.

Nor has the bloodshed in Congo ever struck the same powerful chord as recent events in Somalia, where a new round of bitter fighting has recently erupted. At the end of last year the US backed an Ethiopian invasion of Somalia to topple an Islamic regime that the White House perceived as a possible sponsor of anti-American "terrorists".

The contrasting perceptions of events in Congo and Sudan are ultimately both cause and effect of particular prejudices. Those who argue for liberal intervention, to impose "rights, freedom and democracy", ultimately speak only of their own interests. To view their role in such altruistic terms always leaves them open to well-founded accusations of double standards that damage the international standing of the intervening power and play into the hands of its enemies.

By seeing foreign conflicts through the prism of their own prejudices, interventionists also convince themselves that others see the world in the same terms. This allows them to obscure uncomfortable truths, such as the nationalist resentment that their interference can provoke. This was the case with the Washington hawks who once assured us that the Iraqi people would be "dancing on the rooftops" to welcome the US invasion force that would be bringing everyone "freedom".