Change of State
Of Niccolò Machiavelli's lesser-known works, The Art of War (Dell'arte della guerra), explains effective procedures for the acquisition, maintenance, and use of a military force; he considered Dell'arte della guerra to be his most important work, since it concerned itself solely with war, which to him was the most important aspect of statecraft.

Machiavelli, again, was not alone in history.  The Art of War, a Chinese military treatise attributed to  Sun Tzu , is one of the oldest and most famous studies of strategy.  Sun Tzu, a contemporary Confucius, was a general who lived in the state of Wu in the 6th century BC.   Sun Tzu's treatise stresses subtlety and always making it appear that one is trying to achieve something other than one's actual intention.  As such, Sun Tzu's considerations resemble Machiavelli's corresponding emphasis on deceit and opportunism in The Prince.

In addition to Sun Tzu's work, Carl von Clausewitz's On War is generally acknowledged as one of the historically most significant works on military philosophy.

Sun Tzu Machiavelli von Clausewitz