Will and Ariel Durant
I own this set. As I pass through the 55-year old mark, I keep coming back to it and will read it from start to finish one day. The price is a bargain.
If you want just a taste of the rich content, buy The Lessons of History.
Two other major works I recommend are:
The leadership of civilization building: Administrative and civilization theory, symbolic dialogue, and citizen skills for the 21st century
How to Change the World: Social Entrepreneurs and the Power of New Ideas, Updated Edition