The Battle of Eylau or Battle of Preussisch-Eylau, 7 and 8 February 1807, was a bloody and strategically inconclusive battle between Napoleon's Grande Arme and the Imperial Russian Army under the command of Levin August von Bennigsen near the town of Preussisch Eylau in East Prussia. Late in the battle, the Russians received timely reinforcements from a Prussian division of von L'Estocq. After 1945 the town was renamed Bagrationovsk as a part of Kaliningrad Oblast, Russia. The engagement was fought during the War of the Fourth Coalition, part of the Napoleonic Wars.

Napoleon's armies previously smashed the army of the Austrian Empire in the Ulm Campaign and the combined Austrian and Russian armies at the Battle of Austerlitz on 2 December 1805. On 14 October 1806 Napoleon crushed the armies of the Kingdom of Prussia at the Battle of JenaAuerstedt and hunted down the scattered Prussians at Prenzlau, Lbeck, Erfurt, Pasewalk, Stettin, Magdeburg and Hamelin.

In late January Bennigsen's Russian army went on the offensive in East Prussia, pushing far to the west. Napoleon reacted by mounting a counteroffensive to the north, hoping to prevent their retreat to the east. After his Cossacks captured a copy of Napoleon's orders, Bennigsen rapidly withdrew to the northeast to avoid being cut off. The French pursued for several days and found the Russians drawn up for battle at Eylau.

In a vicious evening clash the French captured the village, with heavy losses on both sides. The following day brought even more serious fighting. Early in the battle a frontal attack by Napoleon failed, with catastrophic losses. To reverse the situation, the emperor launched a massed cavalry charge against the Russians. This bought enough time for the French right wing to throw its weight into the contest. Soon the Russian left wing was bent back at an acute angle and Bennigsen's army was in danger of collapse. A Prussian corps belatedly arrived and saved the day by pushing back the French right. As darkness fell, a French corps tardily appeared on the French left. That night Bennigsen decided to retreat, leaving Napoleon in possession of a snowy battlefield covered with thousands of dead and wounded. Eylau was the first serious check to the Grande Arme, and the myth of Napoleon's invincibility was badly shaken. However, the French would go on to win the war by decisively defeating the Russians on 14 June at the Battle of Friedland.

The Napoleonic Wars (1803–1815) were a series of major global conflicts pitting the French Empire and its allies, led by Napoleon I, against a fluctuating array of European states formed into various coalitions. It produced a period of French domination over most of continental Europe. The wars stemmed from the unresolved disputes associated with the French Revolution and its resultant conflict. The wars are often categorised into five conflicts, each termed after the coalition that fought Napoleon: the Third Coalition (1805), the Fourth (1806–07), the Fifth (1809), the Sixth (1813–14), and the Seventh (1815).

Napoleon, upon ascending to First Consul of France in 1799, had inherited a republic in chaos; he subsequently created a state with stable finances, a strong bureaucracy, and a well-trained army. In December 1805 Napoleon achieved what is considered his greatest victory, defeating the allied Russo-Austrian army at Austerlitz. At sea, the British severely defeated the joint Franco-Spanish navy in the Battle of Trafalgar on 21 October 1805. This victory secured British control of the seas and prevented the invasion of Britain. Concerned about increasing French power, Prussia led the creation of the Fourth Coalition with Russia, Saxony, and Sweden, which resumed war in October 1806. Napoleon quickly defeated the Prussians at Jena and the Russians at Friedland, bringing an uneasy peace to the continent. The peace failed, though, as war broke out in 1809, with the badly prepared Fifth Coalition, led by Austria. At first, the Austrians won a stunning victory at Aspern-Essling, but were quickly defeated at Wagram, which was the bloodiest battle in history until the battle of Leipzig.

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 King of Spain in 1808 as José I. The Spanish and Portuguese revolted with British support and expelled the French from Iberia in 1814 after six years of fighting.

Concurrently, Russia, unwilling to bear the economic consequences of reduced trade, routinely violated the Continental System, prompting Napoleon to launch a massive invasion of Russia in 1812. The resulting campaign ended in disaster for France and the near destruction of Napoleon's Grande Armée.

Encouraged by the defeat, Austria, Prussia, Sweden, and Russia formed the Sixth Coalition and began a new campaign against France, decisively defeating Napoleon at Leipzig in October 1813 after several inconclusive engagements. The Allies then invaded France from the east, while the Peninsular War spilled over into southwestern France. Coalition troops captured Paris at the end of March 1814 and forced Napoleon to abdicate in April. He was exiled to the island of Elba, and the Bourbons were restored to power. But Napoleon escaped in February 1815, and reassumed control of France for around one hundred days. After forming the Seventh Coalition, the allies defeated him at Waterloo in June 1815 and exiled him to the island of Saint Helena, where he died six years later.The Congress of Vienna redrew the borders of Europe and brought a period of relative peace. The wars had profound consequences on global history, including the spread of nationalism and liberalism, the rise of Britain as the world's foremost naval and economic power, the appearance of independence movements in Latin America and 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, as well as civil law. After the end of the Napoleonic Wars there was a period of relative peace in continental Europe, lasting until the Crimean War in 1853.