XX: THE WAR OF THE FOURTH COALITION
Map of Prussia, 1805
King Ludwig I
After the death of Frederick II "der Grosse" (The Great), the Prussian Army stagnated, becoming arrogant and overestimating it's own abilities. It didn't help that the successor of "Old Fritz" was a man that didn't care about the state of the Army at all, giving his duties to the more competent Duke of Brunswick. As result, the Prussians lost the Battle of Valmy and the territories in the Rhineland, to make matters worse, Prince Frederick Wilhelm died of tuberculosis, followed by the death of Frederick Wilhelm II in 1797, the throne was passed to the 24-year old Prince Frederick Ludwig. But Frederich Ludwig I (or Ludwig I) would have a more militaristic outlook, and would put his hands in the dirt to start reforming the Prussian military.Map of Prussia, 1805
King Ludwig I
Ludwig looked at the failure of the Army in the First Coalition War as a chance to reform the Prussian military. But he soon would discover that it was almost impossible, the military establishment blocked the army reforms in order to keep aristocratic privileges. The resistance would soon prove fatal when Prussia and France went to war once again. Inside of Prussia, the "War Party" desired to join a coalition against Napoleon, invading Germany while the Emperor was in the Irish campaign. The King was part of the "Peace Party" who desired to keep the peace, in the King's case, because he knew the army was in no capacity of fighting the French. Two events would pressure the King into war: The Dissolution of the Holy Roman Empire and Hannover.
After almost 900 years of existence, the Holy Roman Empire was dissolved by Napoleon. The last Emperor, Francis II, abdicated his title in order to prevent Bonaparte from claiming it, instead of that, Napoleon dissolved the Empire. In it's place, before going to Ireland, Napoleon created the "Confederation of the Rhine" with himself as Protector, uniting the German States into a massive buffer Confederation to serve as a buffer with Prussia and Austria. The dissolution of the centuries-old German order and the creation of a third power in Germany to serve as a French puppet was outrageous for Prussia.
Napoleon had given Hannover to Prussia after annexing it during the Third Coalition War, as a way to placate the War Hawks in Prussian nobility and keeping peace with Ludwig. But when the French Emperor made peace in Belfast on the 15th of December, he exchanged Hannover for Ireland, and that would mean Prussia would lose its benefit. Hoping to strike a victory before Napoleon came back from Ireland, the War Party finally pressured the King to go to war, one that Ludwig knew that they would lose. An ultimatum was sent to Napoleon retreat from the East bank of the Rhine, of course he refused, and War started on the Christmas of 1806.
The plan by the Duke of Brunswick was to push the Prussian army south to Stuttgart, cutting off the French army and marching west to fight Bonaparte's forces. Initially, the push by the Prussian army was a success, taking Saxony and advancing into Thuringia. The Prussian and French armies had roughly equal numbers, but the French were underestimated by the Prussian Generals, and they would pay heavily for that. Napoleon came back from Ireland, leaving a small force under King Michael I, and organized the Grand Army, marching to meet the Prussians. 120,000 Prussians meet 78,000 French in the Battle of Erfurt, and the Prussians hoped to end Napoleon's reign right there.
That didn't happen, instead, the Prussians were beaten so badly that the entire army organization collapsed, even the Duke of Brunswick died and Ludwig was forced to retreat with the rest of the army to Eastern Prussia. French troops took Berlin in 2 weeks and reached the Vistula by the 6th of February. With the Prussian army collapsing, the Polish population of the Prussian part of the partition rebelled, Napoleon marched into Warsaw as a liberator, even having an affair with Countess Walewska. The Russian army intervened, 80,000 troops under General Benningsen marched to the protection of their ally in Eastern Prussia. Napoleon's army didn't waste time and went into campaign against the Russians in East Prussia, meeting them on the 17th of April in the city of Eylau. After an entire day of battle, Napoleon managed to break the Russian lines with a cavalry charge supported by the Grand Bombard in the center of the Russian lines, 12,000 cavalrymen (including over 2,000 poles) broke the Russian lines and forced them to retreat. The Tsar Alexander asked for a Peace Treaty in Tilsit, ending the 4th Coalition War.
Prussia was forced to give most of its territory to France, with the French carving out the "Duchy of Warsaw" out of the Prussian partition (not including Danzig) as a client state. Tsar Alexander and Napoleon ended up signing an alliance treaty, entering a mutual defense agreement against Great Britain. The Prussians also had to pay heavy reparations, with the destruction of their army and half their territory taken, King Ludwig would finally have the chance to reform the Prussian State deeply. With the help of Gnesienau and Scharnhorst, Prussia would soon make revolutionary changes into the army and administration of the country, preparing themselves to one day have their revenge against Bonaparte.
Map of the Duchy of Warsaw after 1807