was a major turning point in the war thwarting the Austrian attempt to overrun Prussia and bring the conflict to a swift end. In August 1756,
Frederick the Great of Prussia, fearing that his country was about to be overrun and
partitioned by its enemies, launched a pre-emptive strike against Austria's ally,
Saxony, which he succeeded in capturing. That triggered the declaration of the Seven Years' War, and Austria went to war with Prussia with France as an ally. The
Treaty of St Petersburg saw
Sweden and
Russia join the anti-Prussian alliance. Britain was Prussia's only major ally but was at war with France only, not with Austria, Russia, Saxony or Sweden. The alliance reached its high-water mark in late 1757, when a French invasion overran Hanover, Austrian troops recaptured
Saxony, and Austria liberated its own province of
Bohemia, which had been occupied by Prussia. Having signed a
Second Treaty of Versailles in 1757, the French were now committed to an offensive war and sent troops to aid the Austrians against Prussia as well as
financial subsidies to support the large armies put onto the field by Austria. By autumn 1757, the Franco-Austrian forces had appeared to be about to overwhelm the much-smaller Prussia, which would then be partitioned by their allies. However, two decisive Prussian victories at
Rossbach and
Leuthen ended that offensive. France and Austria struggled then to defeat their enemies, as Prussia fought them to a standstill in a conflict that was extremely costly in terms of men, resources and money and brought the French government just at the brink of bankruptcy. While French troops were poured into Germany, Britain went on the offensive against France's overseas empire, capturing French colonies in North America, the West Indies, West Africa and India. France was ultimately forced to abandon its financial commitments to Austria because of a lack of money. France and Austria continued fighting in Germany until late 1762, when an armistice was signed with Britain and Prussia. In 1763, the
Treaty of Paris forced Austria to acknowledge the continued Prussian ownership of
Silesia, and France had to cede a number of colonies to the British. The war was extremely costly and left large swathes of Central Europe in ruins, with little discernible continental advantage for any of the participants. ==Peacetime alliance==