Carl von Clausewitz (1780–1831) was born in Burg, Prussia, and obtained his commission as an officer in the Prussian army at the age of fifteen. He entered the War Academy of Berlin in 1801 and quickly earned a reputation as a brilliant and promising student. When Prussia agreed to become an ally of Napoleon in 1812, Clausewitz joined the Russian army and took part, from the Russian side, in the Campaign of Moscow. He then rejoined his own army and took part in the Battle of Waterloo in 1815. He later became director of the War Academy in Berlin, where he developed his theory of war.