Currently available on Amazon UK for 47p and Amazon US for 75c. Not discounted on Amazon Canada at time of writing but may be worth keeping an eye out.
A Brief History of the Vikings – Jonathan Clements.
UK:
link
US:
link
A Brief History of the Wars of the Roses – Desmond Seward
UK:
link
US:
link
A Brief History of Britain 1485-1660 – Ronald Hutton
UK:
link
US:
link
And finally, less directly related to wargaming, but still of interest to many I hope,
A Brief History of Life in the Middle Ages – Martyn Whittock
UK:
link
US:
link
I obviously haven't read these yet, but I have quite a few books in Robinson Publishing's "A Brief History of" series, and have found them all worth the money. It's worth noting that "brief" in this context simply means a normal book length 250-400 pages or so.