In 1812, Napoleon invaded Russia to compel Alexander I to remain in the Continental System and to remove the imminent threat of Russian invasion of Poland. The Grande Armée, 650,000 men (270,000 Frenchmen and many soldiers of allies or subject powers), crossed the Neman on 23 June 1812. Russia proclaimed a Patriotic War, while Napoleon proclaimed a Second Polish war, but against the expectations of the Poles who supplied almost 100,000 troops for the invasion force he avoided any concessions toward Poland, having in mind further negotiations with Russia. Russia maintained a scorched earth policy of retreat, broken only by the Battle of Borodino on 7 September, when the Russians stood and fought. This was bloody and the Russians eventually retreated, opening the road to Moscow. Field Marshal Mikhail Kutuzov made the decision in order to preserve the army. By 14 September, the French captured Moscow. The Russian governor Prince Rastopchin ordered the city burnt to the ground and large parts of it were destroyed. Alexander I refused to capitulate, and with no sign of clear victory in sight, Napoleon was forced to withdraw from Moscow's ruins. So the disastrous Great Retreat began, with 370,000 casualties largely as a result of starvation and the freezing weather conditions, and 200,000 captured. Napoleon narrowly escaped total annihilation at the Battle of Berezina, but his army was wrecked nevertheless. By December only 20,000 fit soldiers from the main army were among those who recrossed the Neman at Kaunas. By this time Napoleon had abandoned his army to return to Paris and prepare a defence against the advancing Russians.