The is that characteristic, capability, or sources of power from which a military force derives its freedom of action, physical strength, or will to fight.

Center of gravity

Explanation:

According to the German Clausewitz, a Prussian military leader, when attacking, it is important to destroy the so called centers of gravity.

The centers of gravity can be the production and industrial centers, or the propaganda and political centers that fuel the war innitiatives.

It is a military doctrine often used by the US airforce for attacking specific targets. Usually being able to destroy the Center of gravity will precipitate gaining the war, at a high cost for the civil population.