Passage: A common language may have been seen to serve as the basis of a nation, but as contemporary historians of 19th-century Germany noted, it took more than linguistic similarity to unify these several hundred polities. The experience of German-speaking Central Europe during the years of French hegemony contributed to a sense of common cause to remove the French invaders and reassert control over their own lands. The exigencies of Napoleon's campaigns in Poland (1806–07), the Iberian Peninsula, western Germany, and his disastrous invasion of Russia in 1812 disillusioned many Germans, princes and peasants alike. Napoleon's Continental System nearly ruined the Central European economy. The invasion of Russia included nearly 125,000 troops from German lands, and the loss of that army encouraged many Germans, both high- and low-born, to envision a Central Europe free of Napoleon's influence. The creation of student militias such as the Lützow Free Corps exemplified this tendency.The debacle in Russia loosened the French grip on the German princes. In 1813, Napoleon mounted a campaign in the German states to bring them back into the French orbit; the subsequent War of Liberation culminated in the great Battle of Leipzig, also known as the Battle of Nations. In October 1813, more than 500,000 combatants engaged in ferocious fighting over three days, making it the largest European land battle of the 19th century. The engagement resulted in a decisive victory for the Coalition of Austria, Prussia, Russia, Saxony, and Sweden, and it ended French power east of the Rhine. Success encouraged the Coalition forces to pursue Napoleon across the Rhine; his army and his government collapsed, and the victorious Coalition incarcerated Napoleon on Elba. During the brief Napoleonic restoration known as the 100 Days of 1815, forces of the Seventh Coalition, including an Anglo-Allied army under the command of the Duke of Wellington and a Prussian army under the command of Gebhard von Blücher, were victorious at Waterloo (18 June 1815)....

Question: When did Napoleon invade Russia?
1812