 Clausewitz served in the Rhine Campaigns (1793–1794) including the Siege of Mainz, when the Prussian army invaded France during the French Revolution, and fought in the Napoleonic Wars from 1806 to 1815.He entered the "Kriegsakademie" (also cited as "The German War School", the "Military Academy in Berlin", and the "Prussian Military Academy," later the "War College") in Berlin in 1801 (aged 21), probably studied the writings of the philosophers Immanuel Kant and/or Fichte and Schleiermacher and won the regard of General Gerhard von Scharnhorst, the future first chief-of-staff of the newly reformed Prussian Army (appointed 1809).Clausewitz, Hermann von Boyen (1771–1848) and Karl von Grolman (1777–1843) were among Scharnhorst's primary allies in his efforts to reform the Prussian army between 1807 and 1814.