Short answers, pulled from the story.
A military, also known as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, and its main task is usually defined as defence of the state and its interests against external armed threats. Beyond warfare it may be used for internal security, crowd control, emergency services, reconstruction, and national honour guards.
The first recorded use of the word military in English, spelled militarie, was in 1582. It comes from the Latin militaris, from miles, by way of French, though its deeper etymology is uncertain, with one suggestion linking it to a sense of going in a body or mass.
A military may consist of one or more branches such as an army, navy, air force, space force, marines, or coast guard. Its command hierarchy is divided by rank, grouped in descending order of authority as officers such as a colonel, non-commissioned officers such as a sergeant, and the lowest rank, the private.
Personnel may be recruited or conscripted depending on the state, and initial training resocializes recruits for military life, including readiness to injure, kill, and face mortal danger. Individuality is suppressed through shaved heads, issued uniforms, and denied privacy, while full-time service typically lasts between two and six years in Australia, the UK, and the US.
Militaries study victory on three levels: strategic, operational, and tactical. Military strategy is managed by a commander-in-chief over months or years, the operational level coordinates tactics with strategy and was pioneered by the German army before and during the Second World War, and tactics concern engaging the enemy in direct combat over hours or days.
One of the oldest military publications is The Art of War by the Chinese philosopher Sun Tzu, a 13-chapter book written in the 6th century BCE. Two major works from the late Roman period are Taktike Theoria by Aelianus Tacticus and De Re Militari by Vegetius, and Carl von Clausewitz later defined strategy in his book On War as the employment of battles to gain the end of war.