The Anglo-Prussian Alliance was a military alliance created by the Westminster Convention between Great Britain and Prussia which lasted formally between 1756 and 1762 during the Seven Years' War. It allowed Britain to concentrate the majority of its efforts against the colonial possessions of the French-led coalition, while Prussia bore the brunt of the fighting in Europe. It ended in the final months of the conflict, and despite its end, strong ties between the two remained.
The Treaty of Westminster was a treaty of neutrality signed on 16 January 1756 between Frederick the Great of Prussia and King George II of Great Britain, Elector of Hanover. The British fears of a French attack on Hanover were responsible for the development of the treaty. Based on the terms of the agreement, both Prussia and Great Britain would seek to prevent any other foreign power's forces passing through the Holy Roman Empire. That was part of the so-called Diplomatic Revolution.
In practice
Despite the British hope to avoid a war, Frederick launched a pre-emptive strike against Austria in August 1756, overrunning Saxony. However, he was soon faced with an onslaught of enemies including France, Austria, Sweden and Russia and was forced to retreat from Bohemia. By 1757 it appeared that without substantive British assistance, Prussia was about to collapse. Frederick had established a large and well-disciplined army, but it was continually short of money. The British began to send large financial subsidies to support their ally. On 11 April 1758, the two states concluded the Anglo-Prussian Convention, formalising their alliance. Neither side would make peace without consulting the other. Following the occupation of Emden, a British contingent was despatched to the continent to serve with the Duke of Brunswick, a Prussian ally. They served to shield Frederick's western flank, allowing him to focus elsewhere. Under Prussian pressure, the British-backed Hanoverian government repudiated the Convention of Klosterzeven and re-entered the war on Prussia's side. In spite of British aid, the Prussian war effort still nearly collapsed in 1759, despite an Allied victory at the Battle of Minden. However, from then to the end of the war, events turned largely in the favour of the Anglo-Prussian Allies. Britain had enjoyed an Annus Mirablis in 1759 defeating France in Europe, North America and Asia as well as repelling a planned French invasion. Britain won a number of key victories over Spain during 1762, and the Russian Empress died, leading Russia to withdraw from the war against Prussia.
Collapse
It was eventually dissolved in 1762, when Britain withdrew financial and military support for Prussian war aims in Continental Europe. Britain won more favourable terms at the Treaty of Paris, gaining a number of the colonial possessions that it had captured from France and Spain. Prussia was able to retain Silesia but did not achieve the acquisition of further large territories that it had hoped for at the outbreak of war. The two powers made distinctly separate peace agreements to end the war. In the years after the war, their relationship deteriorated, with Prussia rejecting approaches from Britain to form a similar alliance before and during the American War of Independence. Prussia instead concluded a fresh alliance with Russia in 1764, and Britain remained diplomatically isolated. After the American War, Britain and Prussia began to move closer again. They co-operated during the Dutch Crisis in 1787 and, the following year, formed part of a Triple Alliance with the Dutch Republic. Following the outbreak of the French Revolution, Britain and Prussia both took part in the various coalitions formed against France.
