After his father's internal reforms, Frederick II adopted an aggressive foreign policy which caused the rise of the Kingdom of Prussia to a great European power.
The later East Prussia suffered particularly from the Seven Years' War (1756-1763) as it was an important battleground and occupied by Russian troops for several years.
Relations with Poland were permanently strained by the First Partition of Poland in 1772. Due to diplomatic pressure the weakened Kingdom of Poland-Lithuania, which was under Russian supremacy, had to assign important parts of the country to Prussia, Russia and Austria. With the exception of Gdansk and Thorn (today Toruń), Prussia received the "Royal Prussia", which had belonged to Poland since 1466. This created the strategically important land bridge to East Prussia. The new part was called West Prussia; the former Prussia was extended by the Roman Catholic Warmia (Ermland) and was now called East Prussia. Frederick went from being King in Prussia to being King of Prussia.
Illustrations:
1.) Anton Graff (1736-1813) – Portrait of Frederick II, 1781The Prussian king Frederick II offered a contradictory picture, that of a man of Enlightenment and musical freethinker but at the same time a practitioner of aggressive power politics. Under his nickname "Alter Fritz" (Old Fritz) he was revered from early on for his military successes but also as an enlightened monarch and his achievements regarding the rule of law. He left his mark on East Prussia also by the introduction of the potato as an important agricultural crop.
2.) "The Troelfth Cake” (Cake of Kings) – contemporary caricature of the First Partition of Poland in 1772 by Jean-Michel Moreau, a steel engraving by P.L. Vernier, 1810.
Austria-Hungary, Prussia and Russia divided Poland. On the right Frederick II is indicating his claim to the "cake", the Polish map, conversing with Emperor Joseph II. On the far left is Tsarina Catherine II, "the Great" turning to the Polish king Stanisław II August, from whose head the crown is slipping. The partition prevented the great powers from waging war but represented a breach of the law. The reform work of the elected king Stanisław August, who passed the first enlightened constitution of Europe in 1791, suffered a lasting slow-down. In 1793 and 1795 there were two further partitions, at the end of which Poland disappeared as an independent state until 1918. The 1939 Hitler-Stalin Pact is considered by some as the Fourth Partition of Poland, because Poland was divided illegally and by force by its neighbours at the time.