Kenya DOB density plot

Here is a density plot of a sample of Kenyans  based on their year of birth. It's interesting to see the dips correlate with turbulent times; political and military. In the diagram below, the largest unexplained dip is in the early 1970s. Anyone care to explain it; Google and Wikipedia don't return any results?
Click here for a larger image

EDIT:
Could it be the 1969 Kisumu incident?



 


Here is the code used to produce the graph in R