Can you tell me some really good and comprehensive general history sites?

I am writing a paper on Ghana at the moment and I am interested in some historical event that happened in Ghana’s past. While researching Ghana, I found that before 1925, the average life expectancy of someone in Ghana was between the ages of twenty and thirty. Then, in 1925, the average life span began a steady rise until 1991. There were no deviations, just a steady, unbroken rise of the average life span. There was not even a period where the life span plateaued. For that 66 year span, it just rose a little more each year.

This information is not necessary for my paper but it is just so damn interesting that I want to know what triggered this change. So, are there any really comprehensive general history websites out there that might cover this information?