The Kenyatta administration clearly did the most damage in dividing the country along tribal lines and destroying all the national unity that had been achieved in the run up to independence. The historical evidence is there for all to see.
Did you know that for instance that President Kibaki used to represent a Nairobi constituency in parliament? I believe it was what we know today as Makadara constituency.
Tom Mboya also represented a Nairobi constituency. The manner in which the Kenyatta kitchen cabinet/mafia destroyed his political base in Nairobi, along tribal lines, made many Nairobi politicians at the time very nervous and many opted for the safety of their tribal seats back in the rural area. Mwai Kibaki was just one of them.
This single factor had a major effect in ensuring that tribal politics was forever entrenched in Kenya.
It is interesting that people like Njoroge Mungai stuck to Nairobi constituencies, although his situation was unique in that Nairobi's Dagoretti constituency is part of the greater Kiambu district where Mungai and the entire kitchen cabinet hailed from. So technically-speaking it was a rural seat and probably still is when you compare it to all the other parliamentary seats in Nairobi.
It was this kind of politics, pioneered by President Kenyatta's inner circle that destroyed situations like what had been witnessed in 1957 when during the first elections in Kenya...