Here are the sources used in the making of this show. All of them have links to Amazon. Should you purchase any of these books though here it supports the show.  

Allexander the Great by Arrian
One Bullet Away by Nathaniel Fick
On War by Carl von Clausewitz
On Killing by Dave Grossman
What it's like to go to war by Karl Marlantes
The Prince

The Crusades

The Crusader Sates by Malcom Barber
Ibn Al Athir Part 1
Ibn Al Athir Part 2
Medieval Warrior by Martin Dougherty
Chronicle of the First Crusade by Christopher Tyreman
Fuedal Monarcrhy in the Latin Kingdom of Jerusalem by John La Monte
Chronicle of the Third Crusade by Helen Nicholson
The Crusades by Thomas Asbridge
Armies of Heaven by Jay Rubestien
Concise History of the Crusades by Thomas Madden
God's Battalions by Rodney Stark