"Kenya had stayed out of a lot of international competition for various political reasons and Ethiopian had been involved in a big civil war (that eventually spawned Eritrea). That might have something to do with their lack of presence on the international stage."
This is a notoriously known song that can't however hold water. Kenyans, Ethiopians, Somalis, Sudanese and North Africans have been internationally competing since 60's; look at historical lists and you will be surprised, how good they were. Africans boycotted Olympics during the 70's, but they didn't stay off international meetings. Or you have never heard about Henry Rono?! The popular rumour has that because of the boycott, the quality of Africans dropped and it was due to the big investments to athletics in Kenya that their runners again started to excell after the Olympics in Seoul 1988. But historical stats say something completely different: Kenyans started to excel, because their European, North American and Brazilian opponents disappeared virtually overnight around 1985. And as a result, they started to "dominate" with performances, with which they would barely make it to annual Top 10 in mid 80's. Do you want some example?
In the Olympic year 1992, David Kibet from Kenya was the 2nd fastest runner of the year with 3'32"13. But in 1985, Kibet would be only 8th in the annual stats. In other words: There was no "African rising", but "European downfall".
http://ospage2000.ic.cz/800m.htm
http://ospage2000.ic.cz/1500m.htm
Africans actually showed nothing specatacular in the 800/1500 m until 1995 (and when you include only East Africans and omit Morcelli's 3:28'82 from 1992, then the lack of quality is even more surprising), although they routinely occupied 4-6 places in annual Top 10. So why the hell did they explode so late, over a single winter 1995-96? Why did they hide all these genetic marvels in the mountains so long?
In the 3-10 km, the average performances started to rise only after 1990, but they didn't deviate from previous historical trends. Again, the real explosion of times came at the same time like in the 800/1500, in 1995. Why???