The Napoleonic Wars (1803–1815) were a global series of conflicts fought by a fluctuating array of European coalitions against the French First Republic (1803–1804) under the First Consul followed by the First French Empire (1804–1815) under the Emperor of the French, Napoleon Bonaparte. The wars originated in political forces arising from the French Revolution (1789–1799) and from the French Revolutionary Wars (1792–1802) and produced a period of French domination over Continental Europe.^{[page needed]} The wars are categorised as seven conflicts, five named after the coalitions that fought Napoleon, plus two named for their respective theatres: the War of the Third Coalition, War of the Fourth Coalition, War of the Fifth Coalition, War of the Sixth Coalition, War of the Seventh Coalition, the Peninsular War, and the French invasion of Russia.

The first stage of the war broke out when Britain declared war on France on 18 May 1803. After some minor campaigns, Britain allied with Austria, Russia, and several minor powers to form the Third Coalition in April 1805. Napoleon defeated the allied Russo-Austrian armies in the subsequent war which climaxed in French victories at Ulm and at Austerlitz, leading to the dissolution of the Holy Roman Empire and Austria being forced to make peace by the end of the year. Britain and Russia remained at war with France. Concerned about increasing French power, Prussia joined Britain and Russia in the Fourth Coalition, which resumed war in October 1806. Napoleon defeated the Prussians at Jena-Auerstedt and the Russians at Friedland, bringing an uneasy peace to the continent by July 1807, and again leaving Britain as France's sole major enemy. Britain was unable to dispute French dominance on the continent but obtained hegemony over the seas after a string of victories including Trafalgar. Russia used the interim peace to resolve wars with the Ottomans, Swedes, and Iranians.

Hoping to isolate and weaken Britain economically through his Continental System, Napoleon launched an invasion of Portugal, the only remaining British ally in continental Europe. After occupying Lisbon in November 1807, and with the bulk of French troops present in Spain, Napoleon seized the opportunity to turn against his former ally, depose the reigning Spanish royal family, and declare his brother as Joseph I the King of Spain in 1808, to the disapproval of the vast majority of the Spanish populace. Spain subsequently joined Britain and Portugal, with the three powers engaging France in the Peninsular War. The diversion of French armies to the large new Anglo-Spanish front led to Austria reentering the conflict and forming the Fifth Coalition in April 1809, principally composed of Austria, Spain, and Britain. At first, the Austrians won a significant victory at Aspern-Essling but they were quickly defeated at Wagram, forcing the imposition of an even harsher peace in October 1809. Britain, Spain, and Portugal remained at war with France.

Concurrently Russia, unwilling to bear the economic consequences of reduced trade, routinely violated the Continental System, prompting Napoleon to launch a massive invasion in June 1812. The resulting campaign was costly for both sides, but ultimately ended in disaster for France and the near-destruction of Napoleon's Grande Armée. French forces retreated from Russian territory by December 1812 and began reconstituting their lost strength. Encouraged by the defeat, Austria, Prussia, and several minor powers joined Russia, Britain, and Spain in a Sixth Coalition and began a campaign against France. The Sixth Coalition decisively defeated Napoleon at Leipzig in October 1813. The allies then invaded France on two fronts: the Russians, Austrians, and Prussians (plus minor allies) invaded France from the east, while the British, Spanish, and Portuguese (plus minor allies) invaded France from the west. Coalition troops captured Paris at the end of March 1814, forced Napoleon to abdicate in April, exiled him to the island of Elba, and restored power to the Bourbons.

Napoleon escaped from exile in February 1815 and reassumed control of France for around one hundred days, igniting the eponymous conflict. The allies formed the Seventh Coalition, which defeated him at Waterloo in June 1815 and exiled him to the island of Saint Helena, where he died six years later in 1821.

The wars had profound consequences on global history, including the spread of nationalism and liberalism, advancements in civil law, the rise of Britain as the world's foremost naval and economic power, the appearance of independence movements in Spanish America and the subsequent decline of the Spanish and Portuguese Empires, the fundamental reorganization of German and Italian territories into larger states, and the introduction of radically new methods of conducting warfare. After the end of the Napoleonic Wars, the Congress of Vienna redrew Europe's borders and brought a relative peace to the continent, lasting until the Revolutions of 1848 and the Crimean War in 1853.

Napoleon Bonaparte seized power in a coup on 9 November 1799, establishing a military dictatorship. There are numerous 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, declaring 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. Historian Frederick 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.