Military history is composed of the events in the history of humanity that fall within the category of conflict. This may range from a melee between two tribes to conflicts between proper militaries to a world war affecting the majority of the human population. Military historians record (in writing or otherwise) the events of military history.

Military activity has been a constant process over thousands of years, and the essential tactics, strategy, and goals of military operations have been unchanging throughout history. As an example one notable maneuver is the double envelopment, considered to be the consummate military maneuver, executed by Hannibal in the Battle of Cannae in 216 BCover 2,200 years ago. This same maneuver was also described by the Chinese military theorist Sun Tzu, who wrote at roughly the same time as the founding of Rome. By the study of history, the military seeks to not repeat past mistakes, and improve upon its current performance by instilling an ability in commanders to perceive historical parallels during battle, so as to capitalize on the lessons learned. The main areas military history includes are the history of wars, battles, and combats, history of the military art, and history of each specific military service.

There are a number of ways to categorize warfare. One categorization is conventional versus unconventional, where Conventional warfare involves well-identified, armed forces fighting one another in a relatively open and straightforward way without weapons of mass destruction. "Unconventional" refers to other types of war which can involve raiding, guerrilla, insurgency, and terrorist tactics or alternatively can include nuclear, chemical, or biological warfare.

All of these categories usually fall into one of two broader categories: High intensity and low intensity warfare. High intensity warfare is between two superpowers or large countries fighting for political reasons. Low intensity warfare involves counterinsurgency, guerilla warfare and specialized types of troops fighting revolutionaries.

One method of dividing such a massive topic is by cutting it into periods of time. While useful this method tends to be inaccurate and differences in geography mean there is little uniformity. What might be described as ancient warfare is still practiced in a number of parts of the world. Other eras that are distinct in European history, such as the era of Medieval warfare, may have little relevance in East Asia.