The Second Treaty of Tilsit was a pivotal diplomatic agreement signed between Napoleon Bonaparte of France and King Frederick William III of Prussia. Following a series of military confrontations during the War of the Fourth Coalition, the negotiations took place in July 1807 near the Niemen River in what is now Lithuania. The treaty resulted in Prussia conceding approximately half of its territory and ceding significant areas to France's allies. The loss was a major blow to Prussia's prestige and territorial integrity, reshaping the map of Europe substantially.

Napoleon's strategy aimed to isolate Britain and strengthen his influence over continental Europe. The provisions of the treaty not only forced Prussia to recognize the newly established Duchy of Warsaw but also required it to enact military and administrative reforms in line with French interests. This marked a significant moment of transformation for Prussia as it sought to recover from the defeat and restore its position.

The treaty had lasting implications as it contributed to the rise of nationalist sentiments within Prussia. The state's leaders understood the need to modernize their military and state structure, eventually leading to the Prussian reforms that would contribute to its resurgence in the years leading up to the unification of Germany. Additionally, the Treaty of Tilsit played a role in forming a series of alliances that influenced the political landscape of Europe, setting the stage for subsequent conflicts.