There are several great books about Alexander that focus on his astonishing military career but they tend to be scholarly and difficult for the Alexander novice to take in. If you want to get a general overview with lots of illustrations, maps, and photos, then this is the book for you. Alexander the Great has been and remains a lot of different things to different people, but one thing that the great majority can agree on is that he was one amazing general and military commander.
This book focuses on Alexander's army and how it was developed under his father - King Philip II, the weaponry used by the Macedonian army, the campaigns of Alexander in Asia, and a fairly detailed analysis of all the major battles and sieges with colorful maps and illustrations. Seminal titles from military historians like J.F.C. Fuller, Theodore A. Dodge, and Peter G. Tsouras go more in-depth in their analysis of Alexander's military strategies and tactics but they require a lot of imagination and involvement on the readers' part to visualize what happened.
The detailed maps give you a good idea of the scope of the battles and the extent of Alexander's amazing campaigns through Asia. When you consider that the army formations at the front line often stretched well over a mile you get an idea of how massive these battles were. It's really hard to envision leading an army without radio communications into a field that would cover several square miles and the chaos ensuing within, but that's exactly what these battles were like. What is truly amazing is that no one in the history of warfare quite had the spectacular success that Alexander had.
Even with all this information from books such as these, it's hard to pinpoint what made Alexander so successful when so many others have failed miserably or barely made out of battles alive. Alexander not only won these battles against much larger opponents, but he won decisively in routs in which the enemies suffered over 10 times the casualties that Alexander's armies suffered. You look at the battle results and simply go, "Wow! But how?!?" This book gives you a starting point towards understanding Alexander as an unparalleled military commander. If you want an easy-to-read and easy-to-understand book about Alexander's military achievements, this is definitely the book to get you started.