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.
The British quickly enforced a naval blockade of France to starve it of resources. Napoleon responded with economic embargoes against Britain, and sought to eliminate Britain's Continental allies to break the coalitions arrayed against him. The so-called Continental System formed a league of armed neutrality to disrupt the blockade and enforce free trade with France. The British responded by capturing the Danish fleet, breaking up the league, and later secured dominance over the seas, allowing it to freely continue its strategy. Napoleon won the War of the Third Coalition at Austerlitz, forcing the Austrian Empire out of the war and formally dissolving the Holy Roman Empire. Within months, Prussia declared war, triggering a War of the Fourth Coalition. This war ended disastrously for Prussia, defeated and occupied within 19 days of the beginning of the campaign. Napoleon subsequently defeated the Russian Empire at Friedland, creating powerful client states in Eastern Europe and ending the fourth coalition.
Concurrently, the refusal of Portugal to commit to the Continental System, and Spain's failure to maintain it, led to the Peninsular War and the outbreak of the War of the Fifth Coalition. The French occupied Spain and formed a Spanish client kingdom, ending the alliance between the two. Heavy British involvement in the Iberian Peninsula soon followed, while a British effort to capture Antwerp failed. Napoleon oversaw the situation in Iberia, defeating the Spanish, and expelling the British from the Peninsula. Austria, keen to recover territory lost during the War of the Third Coalition, invaded France's client states in Eastern Europe. Napoleon defeated the fifth coalition at Wagram.
Attempts to disrupt the British blockade led to the United States declaring war on Britain, while grievances over control of Poland, and Russia's withdrawal from the Continental System, led to Napoleon invading Russia in June 1812. The invasion was an unmitigated disaster for Napoleon; scorched earth tactics, desertion, French strategic failures and the onset of the Russian winter compelled Napoleon to retreat with massive losses. Napoleon suffered further setbacks; French power in the Iberian Peninsula was broken at Battle of Vitoria the following summer, and a new coalition began the War of the Sixth Coalition.
The coalition defeated Napoleon at Leipzig, precipitating his fall from power and eventual abdication on 6 April 1814. The victors exiled Napoleon to Elba and restored the Bourbon monarchy. Napoleon escaped from Elba in 1815, gathering enough support to overthrow the monarchy of Louis XVIII, triggering a seventh, and final, coalition against him. Napoleon was decisively defeated at Waterloo, and he abdicated again on 22 June. On 15 July, he surrendered to the British at Rochefort, and was exiled to Saint Helena, where he died in 1821. The Treaty of Paris, signed on 20 November 1815, formally ended the war.
The Bourbon monarchy was restored once more, and the victors began the Congress of Vienna, to restore peace to the continent. As a direct result of the war, the Kingdom of Prussia rose to become a great power on the continent, while Great Britain, with its unequalled Royal Navy and growing Empire became the world's dominant superpower, beginning the Pax Britannica. The Holy Roman Empire was dissolved, and the philosophy of nationalism, that emerged early in the war, greatly contributed to the later unification of the German states, and those of the Italian peninsula. The war in Iberia greatly weakened Spanish power, and the Spanish Empire began to unravel; Spain would lose nearly all of its American possessions by 1833. The Portuguese Empire began a rapid decline, with Brazil declaring independence in 1822.
The wars revolutionised European warfare; the application of mass conscription and total war led to campaigns of unprecedented scale, as whole nations committed all their economic and industrial resources to a collective war effort. Tactically, the French Army redefined the role of artillery, while Napoleon emphasised mobility to offset numerical disadvantages, and aerial surveillance was used for the first time in warfare. While not a new tactic, the highly successful Spanish guerrillas demonstrated the capability of a people driven by fervent nationalism, liberalism and religious fundamentalism against an occupying force. Due to the longevity of the wars, and the extent of Napoleon's conquests, the ideals of the French Revolution had a massive impact on European social culture; many subsequent revolutions, such as that of Russia, looked to the French as their source of inspiration, while its core founding tenets greatly expanded the arena of Human rights and shaped modern political philosophies in use today.