On 23 June, 1812 the French Grande Arme, over 600,000 strong and
composed of men from the many nations that had become part of Napoleon's
empire, poured over the Russian border. In defense of Russia, an army of
approximately the same number faced them. The campaign was disastrous
for Napoleon, and it marked the beginning of his decline in power.
Amongst those who participated in the campaign was von Clausewitz. This
renowned Prussian military strategist and historian defected from the
French Army and joined the Russian Imperial headquarters where he spent
the campaign close to the senior Russian officers who made the critical
decisions.
The campaign raised many questions which continue to be debated to this
day and Clausewitz's considered account has long been regarded as a
highly valuable source. His expert analysis of the Battle of Borodino
indicates that he was heavily involved in the engagement as a staff
officer, whose duties would have entailed his constant traveling round
the battlefield.
He was present at the secret Convention of Tauroggen, and his account of
this important treaty and its effect in bringing about the defection of
the Prussian corps from the French is unique.