As Napoleon's fortunes declined, those of his enemies rose; and a coalition, destined to be finally victorious, began to emerge in the chaotic winter of 1812–13. While remnants of the Grande Armée stumbled westward out of Russia, Tsar Alexander I decided to pursue Napoleon beyond Russian soil and out across Europe, seeking allies as Russian arms advanced. Prussia became the first by the Treaty of Kalisch of February 1813, which provided for obvious war needs, and promised to restore Prussia to her former proportions. Austria was slower in responding to Russian advances, but Great Britain signed treaties of alliance and subsidy with both Prussia and Russia at Reichenbach in June. Following a fruitless armistice and a singularly barren ‘peace’ conference at Prague they resumed the struggle against Napoleon in August, this tune in the Germanies and with Austria finally in the coalition. After several secondary engagements, the battle of Leipzig, 16–18 October 1813, demonstrated the impressive power of the coalition by smashing Napoleon's position in Central Europe. His last German allies deserted him, and his army of nearly 200,000 was utterly routed, two-thirds of it killed, wounded, sick or captured. Before the end of the year the French had been confined to territory west of the Rhine for the first time since their eruption in 1805.

The autumn of 1813, so successful in allied military affairs, was a singularly frustrating period for Britain's foreign secretary, Lord Castlereagh. Although his country had been constantly and actively in opposition to Napoleon for years, although she had driven the enemy from Spain, rendered his fleet useless and financed the coalition, scant attention was paid to her counsels by remote allies preoccupied with Napoleon in Central Europe.