The French invasion of Russia began on 24 June 1812 when Napoleon's Grande Armée crossed the Neman River in an attempt to engage and defeat the Russian army. Napoleon hoped to compel the Russian Tsar 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, to gain favor with the Poles and provide a political pretext for his actions. Things didn't work out this way though, and within six months the Grand Armée had lost some 380,000 men dead and 100,000 captured. Napoleon returned to Paris to raise more forces but the campaign effectively ended on 14 December 1812, with the last French troops leaving Russian soil. This campaign was a turning point in the Napoleonic Wars leaving the reputation of Napoleon severely shaken, and the Grande Armée reduced to a fraction of its initial strength. These events triggered a major shift in European politics with Prussia, soon followed by Austria, breaking their imposed alliance with France and switched sides.