the road, and Napoleon was forced to retreat the same way he had come to Moscow, through the heavily ravaged areas along the Smolensk road. In the following weeks, the Grande Armée was dealt a catastrophic blow by the onset of the Russian Winter, the lack of supplies and constant guerrilla warfare by Russian peasants and irregular troops. When the remnants of Napoleon's army crossed the Berezina River in November, only 27,000 fit soldiers survived, with 380,000 men dead or missing and 100,000 captured. Napoleon then left his men and returned to Paris to prepare the defence against the advancing Russians. The campaign effectively ended on 14 December 1812, when the last enemy troops left Russia. The Russians had lost around 210,000 men, but with their shorter supply lines, they soon replenished their armies. For every twelve soldiers of the Grande Armée that entered Russia, only two would make it out in fighting condition. War of the Sixth Coalition, 1812–1814 Seeing an opportunity in Napoleon's historic defeat, Prussia, Sweden, Austria, and several other German states switched sides joining Russia, the United Kingdom and others opposing Napoleon. Napoleon vowed that he would create a new army as large as the one he had sent into Russia, and quickly built up his forces in the east from 30,000 to 130,000 and eventually to 400,000. Napoleon inflicted 40,000 casualties on the Allies at Lützen (2 May 1813) and Bautzen (20–21 May 1813). Both battles involved forces of over 250,000, making them some of the largest conflicts of the wars so far. Metternich in November 1813 offered Napoleon the Frankfurt proposals. They would allow Napoleon to remain Emperor but France would be reduced to its "natural frontiers" and lose control of most of Italy and Germany and the Netherlands. Napoleon still expected to win the wars, and rejected the terms. By 1814, as the Allies were closing in on Paris, Napoleon did agree to the Frankfurt proposals, but it was too late and he rejected the new harsher terms proposed by the Allies. In the Peninsular War, Arthur Wellesley, 1st Duke of Wellington, renewed the Anglo-Portuguese advance into Spain just after New Year in 1812, besieging and capturing the fortified towns of Ciudad Rodrigo, Badajoz, and in the Battle of Salamanca (which was a damaging defeat of the French). As the French regrouped, the Anglo-Portuguese entered Madrid and advanced towards Burgos, before retreating all