Strategy, a word of military origin, refers to a plan of action designed to achieve a particular goal. In military usage strategy is distinct from tactics, which are concerned with the conduct of an engagement, while strategy is concerned with how different engagements are linked. How a battle is fought is a matter of tactics: the terms and conditions that it is fought on and whether it should be fought at all is a matter of strategy, which is part of the four levels of warfare: political goals or grand strategy, strategy, operations, and tactics. Building on the work of many thinkers on the subject, one can define strategy as "a comprehensive way to try to pursue political ends, including the threat or actual use of force, in a dialectic of wills – there have to be at least two sides to a conflict. These sides interact, and thus a Strategy will rarely be successful if it shows no adaptability." Strategy has been extended beyond its traditional fields, military and grand strategy, to business, economics, game theory and other fields.