Anyone interested in the military transformation of Europe and really Eurasia should read John Keegan's excellent "History of Warfare."

https://www.amazon.com/History-Warfare-John-Keegan/dp/067973...

The two best books I've read, which provide the broad historical narrative more so than dates and trivia - Peter Watson's A History from Fire to Freud - http://www.amazon.co.uk/Ideas-history-Freud-Peter-Watson/dp/... and John Keegan's A History of Warfare - http://www.amazon.com/History-Warfare-John-Keegan/dp/0679730...

I don't think either is necessarily the best on the subject, they're just two I've found and found much value from. In addition to allowing me to provide historical stories to make relevant business observations, they (and a History major I suppose) allowed me to write my favourite ever HN comment - http://news.ycombinator.com/item?id=812221