Most observers hoped that the violence that flared up on Kenya following a flawed election Dec. 27 that dubiously returned President Mwai Kibaki to power would eventually calm down. But attacks and counterattacks last weekend in the Rift Valley, most notably in the tourist gateway city of Nakuru, which was considered safe until a few days ago, suggest that the tensions tearing Kenya apart are more deeply rooted than most outside observers had suspected.

The violence is yet more evidence - as if more were needed - that beneath the surface of entities we choose to think of as modern nation-states old ethnic and tribal loyalties, rivalries and hostilities still simmer, ready to boil over when ambitious politicians and would-be leaders stir them with reminders of past grievances and promises of revenge.

If you think such atavistic impulses are confined to "backward" or Third World countries, consider Belgium, whose capital, Brussels, is literally the physical repository of hope for a united European Union in which old-fashioned nationalism will fade away. Belgium has been without a government since June since the Dutch-speaking Flemings and the French-speaking Walloons can't agree on a national candidate, and neither side wants to compromise.

In Kenya the Kikuyu tribe has been dominant in politics and business since the country was a British colony, and the British chose to deal with the country mainly through the Kikuyu. But the land the British colonists chose to make a single country also contained other tribes, principally the Luo but also the Kalenjin. Members of non-Kikuyu tribes have long felt discriminated against and oppressed by the Kikuyu, but the hostility has been kept mostly under wraps.

When the government declared President Kibaki, a Kikuyu, the close winner over opposition leader Raila Odinga, a Luo, riots - apparently stirred by pamphlets and other propaganda urging ethnic killings that began appearing before the election - broke out in the capital of Nairobi and in other cities.

In the month following the election about 800 people have been killed, and at least 200,000 Kenyans have fled their homes. In the beautiful Rift Valley, caravans of Luos heading west pass Kikuyus heading east, as members of the tribes leave formerly mixed neighborhoods that have become deadly and return to ancestral homelands.

It was not out of line for the U.S. ambassador to Kenya, Michael Ranneberger, to hope in public that Kenya would come up with a unity government and reconciliation. But there is little useful that the United States can do to fix the situation, and Kenya is not a core U.S. interest. We feel profound sadness, but little impulse to want to intervene.