Frederick had his spies at every court, who kept him well informed of all the rumors. Apparently in Vienna, Maria Theresa talked openly of re-capturing Silesia with better equipped armies; England and France were at odds over North America and were soon involved in a sea war, and from St. Petersburg the Grand Duke Peter, who idolized Frederick, sent secret dispatches about his aunt's intentions to support Austria. Over all of Europe threatening clouds were on the horizon; it was the quiet before a terrible storm. Frederick decided to surprise the Saxons, and on August 29, 1756, 60000 Prussian troops marched into Saxony. Nobody was prepared for such a sudden outbreak of hostilities. On September 9 his troops invaded Dresden, under strict orders to respect the property of the civilian population.
Unlike other European monarchs, who stayed at home in their castles and palaces, while their generals led their armies into battle, Frederick was his own supreme commander. Forty four years old, he took off his elegant French clothes, and wore his simple field uniform with his tricorne on his head. He was facing a formidable task, one can say, a truly hopeless one: Five nations were opposing him, Austria, France, Russia, Sweden and Saxony-Poland. Four million Prussians against eighty million Allies. The Kaiser even mobilized a West German Reichs army against Prussia. It was not any more just the fight for Silesia, it was clearly the fight of his life for the existence of the kingdom of Prussia. His army was the most well organized and the one best equipped, but the odds were staggering. During the next six and a half years the Prussians fought costly battles in Prague and Kollin, in Rossbach, in Leuthen, in Zorndorf, in Hochkirch, in Kunersdorf, Dresden and Liegnitz, Torgau, Burkersdorf and Schweidnitz. The seven year war should have been called the first world war. When one reads about these endless bloody battles, one can only wonder that even one Prussian soldier was left to fight. At the battle of Liegnitz the Prussians even managed to achieve their first victory after a year and a half. On October 9, 1760, Russian and Austrian troops occupied Berlin. The next day the Austrians behaved like barbarians in the Palaces of Charlottenburg and Schoenhausen. The Austrian general Esterhazy saved the honor of his army when he prevented his men from plundering the Potsdam castle and Sans Souci. A day later they heard that Frederick was own his way with his troops, they were thrown into a panic, and left Berlin that same night; the Russian troops left the city on October 12.
More bloody battles were ahead for Frederick. In January 1762 he would be 50 years old and to his troops he was already "Der Alte Fritz." Then the message from Petersburg reached Frederick: The Tsarina had died, and her nephew had become Tsar Peter III. Peter notified the other European courts, that he would cease all hostilities with the kingdom of Prussia. On May 5 the peace treaty was signed, with Sweden following suit. Peter restored to Frederick all conquered territories and assured him of his friendship. Peter is a small footnote in the history of Europe, but one can say without hesitation, that to a great extent he was the savior of Prussia.
Maria Theresa remained unimpressed. She refused to believe that the new Tsar had gone over to Frederick's side with 20000 Russian troops. In July 1762 Frederick decided to attack the Austrians in Silesia, where he intended to make use of the Russian troops as well. News form Petersburg reached Frederick that little Sophie, whom he had sent to Russia twenty years before to marry the Grand Duke Peter, had Peter III overthrown and had taken the reign over herself as Catherine II. Frederick was stunned.
The Russian general got word from Petersburg to withdraw his troops. Frederick asked the general to postpone the departure of the Russian troops for 3 days, so, if Frederick attacked, the Austrians would not know of the change which had taken place. The Russians agreed and Frederick and his Prussians won the victory at Burkersdorf. Frederick was re-assured when he got word from Catherine that she would continue to honor the peace treaty with Prussia. On October 9 the Austrians capitulated at Schweidnitz. Finally, after losing at Freiberg, Maria Theresa gave in; on December 30, 1762 Prussian and Austrian trustees met at the castle Hubertusburg. The envoy of Saxony was also present. Both sides declined reparation costs. Frederick would keep Silesia, Maria Theresa offered a large sum of money for the return of Glatz, but Frederick did not budge. On February 15, 1763 the Hubertusburger Peace Treaty was signed. The loss of human lives in this war is mind boggling. Frederick did not gain one quadrate meter of new land, but he and his troops had won the battle for the existence of their homeland, the kingdom of Prussia.