Military leadership comprises many aspects, particularly the qualities of the leadership and the responsibility that each rank might have. Additionally, this has an impact on the way the military ranking system is organized, which can be different from country to country. Reforms sometimes make changes to the chain of command by reducing or expanding the size of the military. Certain expectations are imposed on the leadership of the military, where the creativity and fluidity of conditions increase demands on the officers in charge. Military leadership has often been inspirational in the organization of civilian institutions and private corporations. Additionally, the qualities of leadership developed or nurtured in the military context have been adapted to private enterprises and civilian leadership.
The military in the modern context typically divides along the lines of land, air and sea forces (army, air force and navy respectively). Typically, the titles admiral, general and marshal are applied to top-ranking officers. Majors, colonels and captains typically make up the next few tiers of command, followed by lieutenants of various ranks, then first-tier officers and new recruits. Generals, admirals and marshals tend to be the heads of their respective commands, particularly when not at war. Various sub-ranks exist, such as major general or lieutenant general, depending on the country's ranking system. In times of war, command commissions are usually formed that could comprise leadership from the various divisions of the armed forces within one country and might also include equivalent officers in allied militaries. During World War II, there was a Supreme Allied Command under General Dwight D. Eisenhower who directed American, British and Russian maneuvers against the Axis Powers. Lower levels of command exercise the responsibility over other officers who directly manage field operations. From these ranks other, usually younger, officers and deputies are promoted into the higher ranks, typically leaving behind direct combat or operational activity in favor of strategy, management and organization.
The importance of military leadership has been emphasized by numerous thinkers over the course of human history. Sun Tzu, the author of the famed ancient Chinese work, The Art of War, emphasized that responsibility rests on the shoulders of the officers. During a sample demonstration of military organization, he ordered the execution of officers whose subordinates would not take their commands seriously. He emphasized the importance of competent, respected and battle-ready commanders to ensure operational success. He urged commanders to recognize strategic openings and opportunities. He described a list of virtues in the first of the thirteen sections of the work that should be found in or instilled in a military commander. In the introduction to his edition of the ancient work, Ralph Sawyer highlights the five key elements of a good commander as stressed by Sun Tzu: "Wisdom, credibility, benevolence, courage, and strictness." Thus, commanders should be well-educated and experienced in tactics and strategic calculations. Implementation would take courage; commanding the respect of one's troops requires credibility and discipline to address both the fair and unfair demands of subordinates.
Leadership has been professionalized throughout history. In the Islamic era, the plucking of slaves from periphery populations, often Turkic, fed the officers corps. Outstanding children would be taken from their parents, converted to Islam and set to learn the rigors of military command. Those slaves turned into independent commanders, loyal to the state and directly answerable to the imperial rulers. Eventually, these leaders formed their own elite class who attained considerable power and used nepotism to swell the ranks of the professional army with their own relatives. The janissaries and the Mamluks, two of the several examples of slave military classes, became essential parts of their empires in Anatolia and Egypt. This method of recruitment was considered best for maintaining loyalty and discipline.
In the Western world, some form of conscription has been common since the inception of the modern nation-state. After World War II, conscription programs faced decline in numbers since the reduction in the scope of war. In the United States, the experience in Vietnam brought emphasis to the concept of a "professional military" and the use of willing volunteers. Some societies, such as Israel, maintain drafts, with widespread social acceptance paralleling the importance granted in those societies to defense.