With the collapse of the Prussian army, the only major land based military force that the French were fighting was the Russians. Fighting the Russians was not a small endeavor though, they were able to mobilize tons of men and had a great deal of supplies. The French army would be seen as liberators when they entered Poland on their way to fight the Russians. Napoleon would create a new Duchy of Warsaw in Poland and give it to the King of Saxony.
The Russians and French would fight a handful of battles before the decisive end the the 4th Coalition. One of the early battles, the Battle of Eylau (1807), would be fought in the middle of a snowstorm. The weather slowed the reinforcements and would cause Napoleon to retreat instead of fighting a battle that he was outnumbered in. The later Battle Of Heilsberg (1807) would start with the French making tactical mistakes that led them to be trapped against the banks of a river. Just when it looked like the battle was lost the French used their artillery to pound the Russians, who would be forced to retreat under the merciless bombing.
The French army would cause the decisive battle of the war by attacking the Russian army that was retreating from the battlefield at Heilsberg. They attacked as the Russians were crossing the Lyna River and were vulnerable and cause many of the Russian people to drown trying to escape the battlefield. This devastating loss of 20,000 men at the Battle of Friedland (1807) forced the Russians to start the process of peace talks 5 days later.
The Treaty of Tilsit (1807) would end the war and create a tense alliance between the 2 countries. This treaty was actually very equal even though the French had won, in large part because the French weren’t interested in trying to finish off the huge country of Russia. The 2 juggernauts would divide the continent and allow the other side to have full control over what happened in their area. The French allowed the Russians to deal with the Ottomans in whatever way they chose and the Russians let France have the Dalmatian coast and Ionian Islands. The most important decision was the agreement of the Russians to join in the Continental System against the British, which is probably the only thing the French really cared about.
This war would mark the height of Napoleon’s power in Europe, having taken over almost all of western and central Europe by the end of this war. He would place puppet rulers who were dependent on him on the thrones of the German states, including creating the Kingdom of Westphalia to place his brother Jérôme as the King. After the Treaty of Tilsit Britain and Sweden were the only countries left in the war, but when Sweden signed a peace treaty soon after it caused the end of the coalition.