Classical explanations of conventional wars run something like this: An aggressor state seeks political advantage through military force. It has a hunch that the threatened target will likely either make concessions to avoid losing a war, or, if war breaks out, the resulting political gains will be worth the military costs to achieve victory.
Wars then are prevented only by a balance of power and military deterrence: Aggressors have to be warned that it would be stupid to start a war they will likely lose. If there are miscalculations or if emotions run high and logic is ignored, then the resulting conflicts only end when one side loses and has no choice but to accept the imposed terms of the winner.
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