In the War of the Austrian Succession (1740–48) against Maria Theresa, Frederick invaded Silesia without warning, simultaneously offering his aid to Maria Theresa if she ceded a portion of Silesia to him. A brilliant campaigner, Frederick acted with utter disregard of his allies, notably France, and twice concluded separate peace treaties with Maria Theresa (1742, 1745), both times securing Upper and Lower Silesia for Prussia.
In the Seven Years War (1756–63), possession of Silesia was again in dispute; Maria Theresa wished to recover it, and Frederick faced a strong coalition including Austria, Russia, and France. England was his only strong ally. Victorious at Rossbach and Leuthen (1757), he was routed (1759) at Kunersdorf by the Austro-Russian forces, who in 1760 occupied Berlin. In that dark period, it is said, Frederick was on the verge of suicide. However, the accession (1762) of his admirer, Peter III of Russia, took Russia out of the war and opened Frederick's way to victory.
The Peace of Hubertusburg (1763) left Frederick his previous conquests and made Prussia the foremost military power in Europe. He was brilliantly assisted by his principal generals, Seydlitz, James Keith, Ferdinand of Brunswick, Hans Joachim von Zieten, and others. Frederick is widely recognized as the 18th century's greatest general and military strategist. His tactics were studied and admired by Napoleon Bonaparte and exerted great influence on the art of warfare.
After the peace of 1763 Frederick promoted an alliance with Russia, which had nearly defeated him in the Seven Years War. The establishment of a Russo-Prussian alliance prepared the way for the eventual dismemberment of Poland. By the first partition of Poland (see Poland, partitions of) in 1772, Frederick vastly expanded the limits of Prussia. His rivalry with Austria persisted. He opposed any attempts by Austria to extend its power within the Holy Roman Empire and instigated the War of the Bavarian Succession (1778–79) to prevent Austrian annexation of Bavaria. He also created (1785) the Fürstenbund [league of princes] to check Austrian schemes.
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