The Seven Years' War
The Classical Period
Wilhelm Camphausen, Public domain, via Wikimedia Commons
In 1756, there was a great shifting of political alliances in Europe. Great Britain, always looking for a way to protect Hanover from the French, signed an alliance with Prussia. France, which had been Prussia's ally, was furious. Russia, which had been Britain's ally, was also furious, since the rise of Prussian power was a threat to them. Austria, meanwhile, was still eager to recapture Silesia from the Prussians.
Now surrounded by enemies, Frederick II of Prussia launched a preemptive invasion of Saxony, an Austrian ally. Austria was taken completely off guard. Frederick pushed into Bohemia the following year. However, he had to break off the campaign once everyone else got their act together and Prussia was simultaneously attacked by Russia from the east, France and a coalition of German states (the Holy Roman Empire) from the west, and Austria from the south. Although significantly outnumbered, Frederick managed to rout the French and German army in November before turning south and routing the Austrians just a few weeks later.
In addition to being the King of Prussia from 1740 to 1786, Frederick II was also a relatively accomplished musician. He considered involvement in and patronage of the arts essential to his theory of enlightened despotism, where a ruler exercises unlimited legal powers, but is self-restrained in accordance with the laws of reason and justice. (This works great as long as you have a king who is reasonable and just.)
Adolph von Menzel, Public domain, via Wikimedia Commons
When he was not running the Prussian government or performing miracles on the battlefield, Frederick was often found performing as a flautist, often dazzling his admirers with concerti he had composed himself. Frederick's example would inspire the young Austrian Prince Joseph, the son of Maria Theresa, to eventually become a patron for composers like Antonio Salieri and Wolfgang Amadeus Mozart.
The war simmered to a stalemate for the next few years. None of the European powers seemed to be able to beat Frederick's military genius, but Prussia was not strong enough to launch any attacks itself. All the warring nations began to rebuild their armies, but as pressure was kept it up became clear the vastly outnumbered Prussians could not hold out forever.
Then, in 1762, the Russian Empress Elizabeth died, and her son Peter III, who was a great admirer of Frederick, immediately withdrew Russia from the war.
Meanwhile, Great Britain had been fighting French forces basically everywhere except Europe. Taking advantage of the undefeatable Royal Navy, Britain attacked French colonies in the Philippines, India, Africa, the Caribbean, and North America. In Britain's American colonies, the conflict was called the French and Indian War, since many Native American tribes allied themselves with the French against the British and their colonists. By 1762, the constant warfare and harrassment of its colonies had devastated the French economy. Britain then allied with Portugal and declared war on Spain, forcing France to send troops there to defend the Bourbon monarchy. The French war effort against Prussia collapsed, and with his Russian border secure, Frederick was able to focus all his attention on Austria.
In 1763, the depleted powers came to a pair of peace agreements called the Treaty of Paris and the Treaty of Hubertusberg. Britain got some Caribbean colonies, Senegal, and Canada from France, and Florida from Spain. The French were forced to sell cede much of Lousiana to Spain. Prussia returned Saxony to Austria but got to keep Silesia. Everyone was now exhausted and bankrupt except Britain, which was now on a path to world domination.