Military history differs from the history of war, focusing on the people and institutions of war-making, while the latter focuses on the evolution of war itself. Military history has a number of facets, including learning from past accomplishments and mistakes, and creating a sense of military tradition. The Ancient Romans wrote many treatises on warfare, and constructed triumphal arches and victory columns.
Military organization is characterized by a command hierarchy divided by military rank, with ranks grouped as officers, non-commissioned officers, and personnel at the lowest rank. While senior officers make strategic decisions, subordinated personnel fulfil them. Despite the growing importance of military technology, military activity depends above all on people; in 2000 the British Army declared: "Man is still the first weapon of war."
Personnel may be recruited or conscripted, depending on the system chosen by the state. Most military personnel are male, though the proportion of female personnel varies internationally. As of 2017, 50 states still relied partly on individuals under the age of 18 to staff their armed forces. After the US suspended conscription in 1973, the military disproportionately attracted African American men, men from lower-status socioeconomic backgrounds, and men with lower academic records. However, a 2020 study suggests that U.S. Armed Forces personnel are now at parity or slightly higher than the civilian population with respect to socio-economic indicators.
Full-time military employment normally requires a minimum period of service of several years, typically between two and six years. Part-time military employment, known as reserve service, allows a recruit to maintain a civilian job while training under military discipline. Military law introduces offences not recognized by civilian courts, such as absence without leave, desertion, and disrespect. Penalties range from reprimand to imprisonment. Military personnel in some countries have a right of conscientious objection.
Initial training conditions recruits for the demands of military life, including preparedness to injure and kill other people, and to face mortal danger. It is a physically and psychologically intensive process which resocializes recruits. Individuality is suppressed, daily routine is tightly controlled, and continuous stressors deplete psychological resistance.
Military intelligence (MI) involves identifying possible threats. This includes studying the operational environment, hostile and friendly forces, and the civilian population. The difficulty in using military intelligence concepts lies in the secrecy of the information sought, and the clandestine nature of intelligence operatives. Military analysis assesses the military capability of potential aggressors, and provides combat modelling.
Capability development involves determining strategic, operational, and tactical requirements to counter identified threats. It also includes creating design specifications for manufacturers, purchasing systems, and integrating them into the force structure through education and training. Development of military doctrine is arguably the most important of all capability development activities, determining how military forces are used in conflicts.
The development of weapons and military equipment has been closely linked to societal advances. Stone weapons gave way to bronze and iron weapons, and ranged weapons like the sling and bow and arrow were significant advancements. The domestication of the horse and the invention of the wheel also had a major impact. Gunpowder, and later the musket and artillery, redefined firepower. The 20th and 21st centuries saw rapid technological development, including guided missiles, radar, and information technology. Recently, there has been a focus towards the use of renewable fuels for running military vehicles.
For much of military history, the armed forces were considered to be for use by the heads of their societies. Militaries often function as societies within societies, having their own communities, economies, and education systems. Transparency in the military sector is crucial to fight corruption.
Militarism is the belief that a civilian population is dependent upon, and subservient to, its military. Most nations have military laws regulating conduct in war and during peacetime, such as the Geneva Conventions. International protocols restrict the use of certain weapons, and define what constitutes a war crime. Military actions are sometimes justified by furthering a humanitarian cause, known as military humanism.