Leading Article: The worst killing since Cambodia

AID officials now estimate that as many as 500,000 people may have been slaughtered in Rwanda in the past few weeks of organised genocide. It is the greatest man- made disaster since Pol Pot and his henchmen murdered well over 1 million Cambodians. The Cambodian tragedy was no less horrific in its methodology: to save bullets, the Khmer Rouge's victims - essentially anyone educated or of Chinese descent - were bayoneted, clubbed, worked or starved to death. But it was spread over four years, from 1975 to 1979.

The killing in Rwanda, largely by machete, has been compressed into seven weeks, and is still going on. So heavy has the death toll been that the corpses of up to 40,000 Rwandans have been washed into Lake Victoria down the river Kagera, creating a new form of ecological disaster on the lake's shores. All the evidence suggests that the carnage was prepared long in advance by Hutu extremists in the government. Militias were organised, victims identified and targeted. The aim was nothing less than to eliminate members of the once-dominant Tutsi tribe, plus any opposition Hutus who believed in co-operating with them.

Most civil wars involve military fighting between government troops and more or less well-armed insurgents. There has been an element of that in Rwanda, with Tutsis long in exile in neighbouring Uganda returning in 1990 as the Rwandan Patriotic Front to reclaim their share of power and land. In the most over-populated country in Africa, that was bound to aggravate tensions already created by land shortage, erosion and under-nourishment. Yet it seems an inadequate explanation for the ferocity with which Hutu extremists set about systematically ridding their country once and for all of their former overlords.

As in Bosnia, the warring factions had - despite periodic and horrifying blood-lettings - lived virtually on top of each other, inter- marrying and even changing their ethnic identity. It is hard to see how they will be able to coexist again. The RPF claims to be non- ethnic. But, although it has a Hutu chairman, it is in effect a Tutsi force. There are already signs that its discipline is breaking down and that reprisals against the Hutu are beginning.

The latter have always resented their centuries of feudal subordination to the Tutsis, even if there were symbiotic elements in the relationship. Even without the spate of Tutsi revenge killing that now seems likely, they were never likely to accept a return to dominance by a much-reduced Tutsi minority.

The Rwandan tragedy can be seen as an extreme form of the ethnic and factional wars that have broken out - in Europe as well as Africa - since the end of the Cold War. As such it will be a test of the proposed method of United Nations intervention, which is to pay for 5,500 troops from neighbouring countries. But those African troops are likely to arrive too late. They may find all they have to protect is a charnel house, with the RPF celebrating victory over a wasteland.