Napoleon's Russian Campaign

The French invasion of Russia, "Russian Campaign", "Patriotic War of 1812", was a turning point in the Napoleonic Wars. The Grande Armée, made up of French and allied invasion forces, was reduced to a fraction of its initial strength. The campaign effectively ended on 14 December 1812, not quite six months from its outset, with the last French troops leaving Russian soil.
24 June 1812 when Napoleon's Grande Armée of 680,000 soldiers (including 300,000 of French departments) crossed the Neman River in an attempt to engage and defeat the Russian army. Napoleon hoped to compel Tsar Alexander I of Russia to cease trading with British merchants through proxies in an effort to pressure the United Kingdom to sue for peace.
The official political aim of the campaign was to liberate Poland from the threat of Russia. 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, but the Russian army slipped away from the engagement and continued to retreat, leaving Smolensk to burn while Russian cossacks were burning villages and crops to deny the invaders the option of living off the land. These scorched-earth tactics disturbed the French and forced them to rely on a supply system that was incapable of feeding the large army in the field.
The Russian army retreated into Russia for almost three months. On 7 September, the French caught up with the Russians near a small town called Borodino, seventy miles west of Moscow. The battle that followed was the largest and bloodiest single-day action of the Napoleonic Wars, involving more than 250,000 soldiers and resulting in 70,000 casualties. The French gained a tactical victory, but at the cost of 49 general officers and thousands of men. The Russian army withdrew, leaving the French without the decisive victory.
Napoleon entered Moscow a week later. The Russians had evacuated the and burned the city. After staying in Moscow, Napoleon tried once more to engage the Russian army, but the Russians retreated again. 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, bitter cold and persistent attacks upon isolated troops from Russian peasants and Cossacks led to great losses and a loss of discipline in the army. When the remnants of Napoleon's army crossed the Berezina River in November, only 27,000 effective soldiers remained; the Grand Armée had lost some 380,000 men dead and 100,000 captured. Following the crossing of the Berezina, Napoleon left the army after much urging from his advisors and with the unanimous approval of his Marshals. He returned to Paris to protect his position as Emperor and to raise more forces to resist the advancing Russians.
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.