Napoleon sent an army of 600,000 men, some impressed from Prussia, German and Poland, into Russia when the alliance concluded in 1807 by the Treaty of Tilsit broke down. The Russians responded with a scorched-earth policy, retreating before Napoleon and leaving his army nothing to forage.
Editors. "Napoleon marches into Russia". The Literary Encyclopedia. First published 01 February 2010; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=4468, accessed 18 April 2015.]