Carl von Clausewitz

Carl Philipp Gottfried (or Gottlieb) von Clausewitz (1 June 1780 – 16 November 1831) was a Prussian general and military theorist who stressed the "moral" (meaning, in modern terms, psychological) and political aspects of war. His most notable work, Vom Kriege (On War), was unfinished at his death. Clausewitz was a realist in many different senses and, while in some respects a romantic, also drew heavily on the rationalist ideas of the European Enlightenment.

Source: Carl von Clausewitz on Wikipedia.