The Baron Antoine Henri de Jomini's "The Art of War" is an early classic on military strategy and tactics. With von Clausewitz, he was one of the more widely read scholars on the subject in the 19th century. His book tends to have an abstract, scholarly air to it that suggests that he was more of an "arm chair" theorist than a man whom he learned much from--Napoleon Bonaparte. Napoleon may have had general perspectives on warfare, but he was also someone who was able to be improvisational on the battlefield, and Jomini cannot quite capture that in this work. Nonetheless, a classic.
Charles Messenger's Introduction does single out Jomini for mention, when he notes (Page v): "Nineteenth -century military thought was dominated by two men, one a German and the other a Swiss. . . . They were von Clausewitz and Jomini." Jomini argued that (Page vii): "Strategy decodes where to act; logistics brings the troops to this point; grand tactics determines the manner of execution and the employment of the troops."
As Jomini's actual work begins, he identifies the six key components of the art of war (Page 2):
"1. Statesmanship in its relation to war.
2. Strategy, or the art of properly directing masses upon the theater of war, either for defense or for invasion.
3. Grant tactics.
4. Logistics, or the art of moving armies.
5. Engineering--the attack and defense of fortifications.
6. Minor tactics."
The book itself, then, considers these elements of the art of war. No need to go into great detail. But some general points are in order. At one point, he emphasizes the importance of "lines"--interior lines, where one side has a more compact line and can move troops from one point to another with greater facility than the enemy; exterior lines, which are longer. If a smaller force, interior lines are critical; if a larger force, exterior lines may prove no impediment to success.
One facet of this book is his diagrams depicting various orders of attack (pages 188 and following). This tends, as noted earlier, to be pretty abstract. One hesitates to think that officers in the heat of combat will intellectually assess the various orders of attack and rationally choose one over another. Among these are straight linear orders (where the two forces approach one another in straight lines) to "en echelon" attacks, where the lines are arrayed in depth.
He notes in his conclusion that (Page 321) "War in its ensemble in not a science, but an art."
So, if one might be interested in an analysis of military strategy and tactics from the early part of the 19th century, this is not a bad starting point. It is a classic on the subject, and, even if too abstract and academic, can be a useful book to understand the military in that era.