Prussia begins the War of the Fourth Coalition against France.

The Kingdom of Prussia was a German state that existed from 1701 to 1918. It played a significant role in the unification of Germany in 1871 and was a major constituent of the German Empire until its dissolution in 1918. Although it took its name from the region called Prussia, it was based in the Margraviate of Brandenburg. Its capital was Berlin.

The War of the Fourth Coalition was a war spanning 1806–1807 that saw a multinational coalition fight against Napoleon's French Empire, subsequently being defeated. The main coalition partners were Prussia and Russia with Saxony, Sweden, and Great Britain also contributing. Excluding Prussia, some members of the coalition had previously been fighting France as part of the Third Coalition, and there was no intervening period of general peace. On 9 October 1806, Prussia declared war on France and joined a renewed coalition, fearing the rise in French power after the defeat of Austria and establishment of the French-sponsored Confederation of the Rhine in addition to having learned of French plans to cede Prussian-desired Hanover to Britain in exchange for peace. Prussia and Russia mobilized for a fresh campaign with France, massing troops in Saxony.

The French Empire, known retroactively as the First French Empire, was the empire ruled by Napoleon Bonaparte, who established French hegemony over much of continental Europe at the beginning of the 19th century. It lasted from 18 May 1804 to 6 April 1814 and again briefly from 20 March 1815 to 7 July 1815, when Napoleon was exiled to Saint Helena.