Napoleonic Wars (1803–15), fought by France after Napoleon I became emperor. After the Treaty of Amiens (1802), which had ended the French Revolutionary Wars (1792–1802), Britain declared war on France (1803), maintaining that Napoleon was not keeping the treaty. Napoleon planned to invade Britain, but the British fleet proved too strong for him, especially after the Battle of Trafalgar (1805). The British, Swedes, Austrians, and Russians formed an alliance (July 1805); Napoleon defeated the Austrians and Russians at Austerlitz (Dec. 1805), the Prussians at Jena (1806), and the Russians at Friedland (1807); the Peace of Tilsit (1807) left him nearly master of Europe. Meanwhile, Britain had secured supremacy of the seas at Trafalgar. The Continental System begun after Jena was Napoleon's attempt to blockade British trade; on the pretext of enforcing it he invaded Portugal (1807) and Spain (1808). During the defeat of his armies by the British in the Peninsular War (1808–14), he signed the Peace of Schönbrunn (1809) with the defeated Austrians. In 1812 Napoleon invaded Russia with an army of some 500,000. He barely won the Battle of Borodino (1812) and marched unchallenged to Moscow, but his troops suffered from lack of supplies and the cold weather. Their retreat from Moscow and Russia was horrifying; only about 30,000 of Napoleon's soldiers returned. The French, by now drained of manpower and supplies, were decisively beaten at Leipzig (1813). Paris fell, and on April 11, 1814, Napoleon abdicated. The victorious allies signed the Treaty of Paris with the Bourbons. After Napoleon's escape from Elba and return (the Hundred Days) and his defeat at Waterloo (1815), the second Treaty of Paris was signed (1815).