French invasion of Russia - Wikipedia

On June 24, 1812, Napoleon crosses the Neman River and invades Russia.
From the article:
"The Grande Armée was a very large force, numbering 680,000 soldiers (including 300,000 of French departments). It was the largest army ever assembled in the history of warfare up to that point.[17] Through a series of long marches Napoleon pushed the army rapidly through Western Russia in an attempt to bring the Russian army to battle, winning a number of minor engagements and a major battle at Smolensk in August. Napoleon hoped the battle would win the war for him, but the Russian army slipped away and continued the retreat, leaving Smolensk to burn.[18] French plans to quarter at Smolensk were abandoned, and Napoleon pressed his army on after the Russians.[19] As the Russian army fell back, the Cossacks applied scorched-earth tactics, burning down villages, towns and crops and forcing the French to rely on a supply system that was incapable of feeding the large army in the field.[15][20]

The Russian army retreated into Russia for almost three months. In response to the loss of territory, the commander of the Russian army, Field Marshal Barclay, was replaced by Prince Mikhail Kutuzov on 29 August. On 7 September, the French caught up with the Russian army which had dug itself in on hillsides before a small town called Borodino, seventy miles west of Moscow. The battle that followed was the bloodiest single-day action of the Napoleonic Wars, with 72,000 casualties, and a narrow French victory. The Russian army withdrew the following day, leaving the French without the decisive victory Napoleon sought.[21] A week later, Napoleon entered Moscow, which the Russians had abandoned and burned.[22] The loss of Moscow did not compel Alexander I to sue for peace, and both sides were aware that Napoleon's position grew worse with each passing day. Napoleon stayed on in Moscow for a month, waiting for a peace offer that never came. On 19 October, Napoleon moved his army out southwest toward Kaluga, where Kutuzov was encamped with the Russian army.

After an inconclusive battle at Maloyaroslavets, Napoleon continued the retreat. In the weeks that followed the Grande Armée starved and suffered from the onset of the Russian Winter. Lack of food and fodder for the horses, hypothermia from the bitter cold and persistent attacks upon isolated troops from Russian peasants and Cossacks led to great losses in men, and a general loss of discipline and cohesion in the army. More fighting at Vyazma and Krasnoi resulted in further losses for the French. When the remnants of Napoleon's main army crossed the Berezina River in late November, only 27,000 effective soldiers remained; the Grande Armée had lost some 380,000 men dead and 100,000 captured.[23] Following the crossing of the Berezina, Napoleon left the army after much urging from his advisors and with the unanimous approval of his Marshals.[24] He returned to Paris by carriage and sledge to protect his position as Emperor and to raise more forces to resist the advancing Russians. The campaign effectively ended on 14 December 1812, not quite six months from its outset, with the last French troops leaving Russian soil.

The campaign was a turning point in the Napoleonic Wars.[1] It was the greatest and bloodiest of the Napoleonic campaigns, involving more than 1.5 million soldiers, with over 500,000 French and 400,000 Russian casualties.[12] The reputation of Napoleon was severely shaken, and French hegemony in Europe was dramatically weakened. The Grande Armée, made up of French and allied invasion forces, was reduced to a fraction of its initial strength. These events triggered a major shift in European politics. France's ally Prussia, soon followed by Austria, broke their imposed alliance with France and switched sides. This triggered the War of the Sixth Coalition.[2]"