By Mark Doyle
BBC World Affairs Correspondent
The Rift Valley is a geographical fault line that runs through Kenya.
But it is also the centre of a political and ethnic divide.
So it is no coincidence, historians and academics say, that Rift Valley towns like Nakuru and Naivasha have exploded in the wake of Kenya's disputed elections.
They say that while the dispute over the elections is clearly political - with the opposition and some independent observers accusing the government of having rigged the polls - the root cause of some of the violence is hunger for fertile land.
And they add that land hunger is inevitably expressed, in poor communities, through ethnicity or tribe.
A Nairobi-based academic, who spoke on condition of anonymity, said the Rift Valley was dominated, before the advent of large scale commercial farming in Africa, by ethnic Masaai herders and Kalenjin people.
"The Masaai were displaced from the late 19th Century onwards, at least from the more desirable land, by British settlers," the academic said.
The cooler and more fertile parts of the Rift were part of what became known as the "White Highlands" of Kenya.
"When independence came," the academic said, "the departing white farmers were replaced not by Masaai, but to a large extent by politically well-connected Kikuyus."
This displacement - or more accurately the historic resentment that politicians can extract from it - is part of the root of today's violence.
The Kikuyu are the largest and most economically-dominant ethnic group in Kenya. They organised most successfully against the British (in the Mau Mau rebellion and later through elections) so they won the first fruits of independence.
They have been at the heart of the violence in Rift Valley towns like Naivasha and Nakuru - as both perpetrators and victims.
The incumbent government in Kenya is perceived by the opposition as being Kikuyu-dominated, so the current political dispute is fuel for the smouldering embers of a land dispute which has existed for decades.
But the Nairobi-based academic said it was far from being a simple matter of ethnicity.
"Focussing on the Kikuyu is easy," he said "but it's really about deep, long-running income inequalities in Kenya" - and a rapidly growing population which sees land ownership as a means of survival.
Rich and politically well-connected members of the Masaai community, he stressed, had benefited from land ownership in the Rift Valley as well as Kikuyus.
Politicians from all ethnic groups, the academic said, had been preparing the ground for trouble in the wake of the elections because they know that "land clashes", as they are known in Kenya, always flare up around polling time.
"There were peaks in land clash violence 1992/3, 1997 and 2001/2", he said, "all around election time."