Prussia enjoyed a brief moment of glory under King Fredrick but that glory was cut brutally short during the Third War of Supremacy [1756-1760] with Fredrick dying at the Battle of Kunersdorf and his army being cut to pieces. In the aftermath of the war, Prussia lost not only Silesia but also large amounts of its original territory with Saxony being the primary beneficary. However between 1767 and 1771, Prussia fought alongside Russia against Austria and was able to secure a personal union with the Kingdom of Poland. This secured Prussia's position for the time being but neither restored its former status as one of the great powers of Europe and tied it to a rebellious land which disliked King Frederick William II.
Prussia rallied alongside Saxony and the other German states against France in the late 1790s but after the death of King Frederick William II, Poland revolted and Prussia became dragged into a war with Saxony. While Prussia was arguably still more powerful than Saxony, it was unable to win a two-front war thanks to a series of poor military decisions and poor luck. The entry of Denmark-Sweden into the war on the side of Saxony further strained the Prussian military. In September 1802, with Prussia west of the Elbe occupied, a coup led to the death of King Frederick William III and the Prussian state fracturing. In May 1804, the treaty of Berlin stripped Prussia of its lands inside the Holy Roman Empire and divided the Electorate of Brandenberg between Saxony and Mecklenburg. Outside the Holy Roman Empire, Prussia also lost Danzig and Kognisberg to Denmark-Sweden.
Despite these losses, Prussia would survive as a rump state until its last king, Frederick III attempted to retake his position by occupying Berlin which had experienced a Schimdist revolt. However the Prussian Army was too weak to defeat the republicans in the city and the resulting battle shattered the Prussian army, while seriously wounding the King. The king was forced to flee to Hannover where good medical attention could be sought, and without him and his army, Prussia disintergrated. At the Congress of Brussels, the last remnants of Prussia were annexed by the Polish state although King Frederick himself would continue to play an important role in world events.