A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g. communism during cold war era, supporting or promoting economic expansion through imperialism, and as a form of internal social control. As an adjective the term "military" is also used to refer to any property or aspect of a military. Militaries often function as societies within societies, by having their own military communities.

The profession of soldiering as part of a military is older than recorded history itself. Some of the most enduring images of the classical antiquity portray the power and feats of its military leaders. The Battle of Kadesh in 1274 BC was one of the defining points of Pharaoh Ramesses II's reign and is celebrated in bas-relief on his monuments. A thousand years later the first emperor of unified China, Qin Shi Huang, was so determined to impress the gods with his military might that he was buried with an army of terracotta soldiers. The Romans were dedicated to military matters, leaving to posterity many treatises and writings as well as a large number of lavishly carved triumphal arches and victory columns.