"Machiavelli taught Europe the art of war; it had long been practiced, without being known." Voltaire
The Art of War, one of the few major works of Machiavelli published in his lifetime, is an interesting discussion of how armies should be armed and organized.
Excerpt:
No proceeding is better than that which you have concealed from the enemy until the time you have executed it. To know how to recognize an opportunity in war, and take it, benefits you more than anything else. Nature creates few men brave, industry and training makes many. Discipline in war counts more than fury.