This year England is celebrating the 950th anniversary of the Battle of Hastings.
So I nominate
William the Conqueror by Edward Augustus Freeman.
Amazon's lead reviewer called it "William 101...The text is easy yet very informative."
Kindle - free
https://www.amazon.com/William-Conqu...dp/B004TPFP5C/
Kobo - 99 cents
https://store.kobobooks.com/en-us/eb...e-conqueror-29
B&N Nook - 99 cents
http://www.barnesandnoble.com/w/will...=9781531288495