Now, Kenya is one of the most densely populated countries in Africa with a relatively high population growth rate, and that makes for trouble in Kenya compared to Tanzania.

NPR: Tribalism and Stability in Kenya

In 1960 the republic's population was down to around 2.8m, the lowest in two centuries and a pale shadow of the 8m (for the whole island) in 1840, when this was one of the most densely populated countries in Europe.

ECONOMIST: The luck of the Irish

Many variables explain this, but the most important is that farming in these heavily populated countries (unlike that in America) emits huge amounts of ammonia.

ECONOMIST: Planes and pollution