Napoleon, upon ascending to First Consul of France in 1799, had inherited a chaotic republic; he subsequently created a state with stable finances, a strong bureaucracy, and a well-trained army. In 1805, Austria and Russia waged war against France. In response, Napoleon defeated the allied Russo-Austrian army at Austerlitz in December 1805, which is considered his greatest victory. At sea, the British inflicted a severe defeat in the Battle of Trafalgar in October 1805 upon the joint Franco-Spanish navy, securing British control of the seas and preventing the invasion of Britain itself. Prussian concerns about increasing French power led to a resumption of war in October 1806. Napoleon quickly defeated the Prussians, and defeated Russia in June 1807, bringing an uneasy peace to the continent. The peace failed, though, as war broke out in 1809, and a new coalition was soon defeated.
Hoping to isolate Britain economically, Napoleon invaded Iberia, declaring his brother Joseph king of Spain in 1808. The Spanish and Portuguese revolted with British support, and, after six years of fighting, expelled the French from Iberia in 1814. Concurrently, Russia, unwilling to bear economic consequences of reduced trade, routinely violated the Continental System, enticing Napoleon to launch a massive invasion of Russia in 1812. The resulting campaign ended with the dissolution and withdrawal of the French Grande Armée. Encouraged by the defeat, Prussia, Austria, and Russia began a new campaign against France, decisively defeating Napoleon at Leipzig in October 1813 after several inconclusive engagements. The Allies then invaded France, capturing Paris at the end of March 1814 and forcing Napoleon to abdicate in early April. He was exiled to the island of Elba, and the Bourbons were restored to power. However, Napoleon escaped in February 1815, and reassumed control of France. The Allies responded with the Seventh Coalition, defeating Napoleon permanently at Waterloo in June 1815 and exiling him to St Helena.
The Congress of Vienna redrew the borders of Europe, and brought a lasting peace to the continent. The wars had profound consequences on global history; it fostered the spread of nationalism and liberalism, saw the rise of the British Empire as the world's foremost power, independence movements in Latin America and the subsequent collapse of the Spanish Empire, the fundamental reorganisation of German and Italian territories into larger states, and the establishment of radically new methods of conducting warfare.
Napoleon seized power in 1799, creating a de facto military dictatorship. There are a number of opinions on the date to use as the formal beginning of the Napoleonic Wars; 18 May 1803 is often used, when Britain and France ended the only short period of peace between 1792 and 1814. The Napoleonic Wars began with the War of the Third Coalition, which was the first of the Coalition Wars against the First French Republic after Napoleon's accession as leader of France.
Britain ended the Treaty of Amiens and declared war on France in May 1803. Among the reasons were Napoleon's changes to the international system in Western Europe, especially in Switzerland, Germany, Italy and the Netherlands. Kagan argues that Britain was irritated in particular by Napoleon's assertion of control over Switzerland. Furthermore, Britons felt insulted when Napoleon stated that their country deserved no voice in European affairs, even though King George III was an elector of the Holy Roman Empire. For its part, Russia decided that the intervention in Switzerland indicated that Napoleon was not looking toward a peaceful resolution of his differences with the other European powers.