A commander-in-chief is the person or body that exercises supreme operational command and control of a nation's military forces or significant elements of those forces.
The military, also called the armed forces, are forces authorized to use deadly force, and weapons, to support the interests of the state and some or all of its citizens.
Command generally refers to the ability to "dominate an area of situation".
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In the latter case, the force element is those forces within a particular region, or associated by function.
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As a practical term; it refers to military competencies that reside in a nation-state's executive leadership—either a head of state, a head of government, a minister of defence, a national cabinet, or some other collegial body.
The title Defence Minister, Minister for Defence, Secretary of Defense, Secretary of State for Defence, Secretary of National Defense or some similar variation, is assigned to the person in a cabinet position in charge of a Ministry of Defence, which regulates the armed forces in sovereign states.
Head of government is a generic term used for either the highest or second highest official in the executive branch of a sovereign state, a federated state, or a self-governing colony who often presides over a cabinet.
A head of state or Chief of State is the highest-ranking position in a sovereign state and is vested with powers to act as the chief public representative of that state.
Often, a given country's commander-in-chief need not be or have been a commissioned officer or even a veteran.
This follows the principle of civilian control of the military.
Civilian control of the military is a doctrine in military and political science that places ultimate responsibility for a country's strategic decision-making in the hands of the civilian political leadership, rather than professional military officers.