Reddit reviews The Mask of Command

From the ancient and classical ages through the early middle ages, rulers often justified their claims to the throne by their ability to lead men in combat, and had to place themselves at the forefront of battles in order to maintain the respect of their subordinates. Later, as armies grew larger and battles became both more dangerous and more confused (gunsmoke, noise, etc), commanders would have to hang back and direct rather than lead outright. The late, great John Keegan's book The Mask of Command tells the tale of this transition, from Alexander to Hitler.

And as to why they didn't all get killed immediately, I would imagine that part of the reason is the historic practice of capturing enemy nobility for ransom. Also, a leader suck as Alexander the Great, even when leading his army from the front, would be attacking opposing knights on horseback, not the mass of footsoldiers that comprised the majority of both armies. That's where the glory and honor was.

Allow me to recommend picking up a copy of John Keegan's The Mask of Command.

Concepts of courage on the battlefield change with the technology and its use in warfare. John Keegan has written two books that touch on this - The Face of Battle and The Mask of Command

Non-Fiction:

Alexander, I did not read this one, but I did enjoy his chapter on Alexander in the same author's book, The Great Captains.

The Mask of Command, while not only about Alexander, it's hard to go wrong with Kegan.

If you're interested in some historical fiction, try Steven Pressfield's The Virtues of War.

The Mask of Command was a book that I read. Other books on the CMC's reading list dealt with leadership, though not as exclusively as that one. I did the Marine Corps Institute courses up to 8xxx series on leadership. I don't know what else would be relevant specifically to your studies.