This YouTube educational channel is excellent:
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CGP Grey (5 minutes)
https://youtu.be/KW0eUrUiyxo
American Empire (6 minutes)
CGP Grey
https://youtu.be/ASSOQDQvVLU
Death & Dynasties (Rules for Rulers Follow-up) (5 minutes)
CGP Grey
https://youtu.be/ig_qpNfXHIU
All of CGP Grey's Videos in Chronological Order
CGP Grey
http://www.youtube.com/playlist?list=PLqs5ohhass_QhOSkrNqPFEAOv5fBzTvWv