The Seven Years' War, 1756 to 1763, was a global conflict fought by numerous great powers, primarily in Europe, with significant subsidiary campaigns in North America and the Indian subcontinent. The primary warring states were Great Britain and Prussia fighting against France and Austria, with other countries joining these coalitions: Portugal, Spain, Sweden, and Russia, plus Saxony and many other minor states of the Holy Roman Empire. Related conflicts include the Third Silesian War, French and Indian War, Third Carnatic War, Anglo-Spanish War (1762–1763), and Spanish–Portuguese War.
Although the War of the Austrian Succession ended with the Treaty of Aix-la-Chapelle (1748), none of the signatories were happy with the terms, and it was generally viewed as a temporary armistice. It led to a strategic realignment known as the Diplomatic Revolution that ended the long-running rivalry between Austria and France. The two declared war on Britain after signing the Treaty of Versailles in 1756, with a second agreement in 1757 bringing Prussia into the war on the side of Britain.
Spain became a French ally in 1762, unsuccessfully invading Portugal, and losing Havana and Manila to Britain. Although these were returned under the Treaty of Paris in 1763, France lost its possessions in North America, while Britain established its commercial dominance in India.
The conflict in Europe centred on Austrian attempts to recover Silesia, and ended with the Treaty of Hubertusburg in 1763. This confirmed Prussian occupation of Silesia and its status as a great power, challenging Austria for dominance within Germany and altering the European balance of power.
The boundary between British and French possessions in North America was largely undefined in the 1750s. France had long claimed the entire Mississippi River basin. This was disputed by Britain. In the early 1750s the French began constructing a chain of forts in the Ohio River Valley to assert their claim and shield the Native American population from increasing British influence.
The British settlers along the coast were upset that French troops would now be close to the western borders of their colonies. They felt the French would encourage their tribal allies among the North American natives to attack them. Also, the British settlers wanted access to the fertile land of the Ohio River Valley for the new settlers that were flooding into the British colonies seeking farmland.
The most important French fort planned was intended to occupy a position at "the Forks", where the Allegheny and Monongahela rivers meet to form the Ohio River in present-day Pittsburgh, Pennsylvania. Peaceful British attempts to halt this fort construction were unsuccessful, and the French proceeded to build the fort they named Fort Duquesne. British colonial militia from Virginia accompanied by Chief Tanacharison and a small number of Mingo warriors were sent to drive them out. Led by George Washington, they ambushed a small French force at Jumonville Glen on 28 May 1754 killing ten, including commander Joseph Coulon de Jumonville. The French retaliated by attacking Washington's army at Fort Necessity on 3 July 1754 and forced Washington to surrender. These were the first engagements of what would become the worldwide Seven Years' War.
Britain and France did not negotiate a solution after receiving news about the clash. The two countries eventually sent regular troops to North America to enforce their claims. The first British action was the assault on Acadia on 16 June 1755 in the Battle of Fort Beauséjour, which was immediately followed by their expulsion of the Acadians. In July, British Major General Edward Braddock led about 2,000 regular army troops and provincial militia on an expedition to retake Fort Duquesne, but the expedition ended in disastrous defeat. In further action, Admiral Edward Boscawen fired on the French ship Alcide on 8 June 1755, capturing it and two troop ships. In September 1755, British colonial and French troops met in the inconclusive Battle of Lake George.
The British navy harassed French shipping beginning in August 1755, seizing hundreds of ships and capturing thousands of merchant seamen even though the two nations were nominally at peace. Incensed, France prepared to attack Hanover, whose prince-elector was also the King of Great Britain and Menorca. Britain concluded a treaty with Prussia in which the latter agreed to protect Hanover. In response France concluded an alliance with its long-time enemy Austria, an event known as the Diplomatic Revolution.
In the War of the Austrian Succession, which lasted from 1740 to 1748, the Prussian King Frederick II had seized the prosperous province of Silesia from Austria. Empress Maria Theresa of Austria had signed the Treaty of Aix-la-Chapelle in 1748 in order to gain time to rebuild her military forces and to forge new alliances.
The War of the Austrian Succession had seen the belligerents aligned on a time-honoured basis. France's traditional enemies, Great Britain and Austria, had coalesced just as they had done against Louis XIV. Prussia, the leading anti-Austrian state in Germany, had been supported by France. Neither group, however, found much reason to be satisfied with its partnership: British subsidies to Austria produced nothing of much help to the British, while the British military effort had not saved Silesia for Austria. Prussia, having secured Silesia, came to terms with Austria in disregard of French interests. Even so, France concluded a defensive alliance with Prussia in 1747, and the Duke of Newcastle, British secretary of state in the 1743–1754 ministry of his brother Henry Pelham, deemed the maintenance of the Anglo-Austrian alignment after 1748 as essential. The collapse of that system and the aligning of France with Austria and of Great Britain with Prussia constituted what is known as the "Diplomatic Revolution" of 1756.
In 1756 Austria was making military preparations for war with Prussia and pursuing an alliance with Russia for this purpose. On 2 June 1746, Austria and Russia had signed the 1746 Treaty of Saint Petersburg,
a defensive alliance that covered their own territories and Poland against attack by Prussia or by the Ottoman Empire. Vienna and Saint Petersburg also agreed to a secret clause on April 22nd 1756 that aimed to destroy any chance of Prussian dominance via a partition. In this proposed partition, Austria was promised the restoration of Silesia and of the countship of Glatz (now Kłodzko, Poland) to Austria and giving East Prussia to Russia and exchanged with the Polish-Lithuanian Commonwealth for the cession of the Polish Duchy of Courland to Russia and other territory near the border. Alexey Bestuzhev-Ryumin, grand chancellor of Russia from 1744 to 1758 under Empress Elizabeth, was hostile both to France and to Prussia, but he could not persuade Austrian statesman Wenzel Anton von Kaunitz to commit to offensive designs against Prussia so long as Prussia was able to rely on French support.
The Hanoverian King George II of Great Britain was passionately devoted to his family's continental holdings, but his commitments in Germany were counterbalanced by the demands of the British colonies overseas. If war against France for colonial expansion were to resume, then Hanover had to be secured against Franco-Prussian attack giving East Prussia to Poland. France was very much interested in colonial expansion and was willing to exploit the vulnerability of Hanover in war against Great Britain, but it had no desire to divert forces to Central Europe for Prussia's interest.
French policy was, moreover, complicated by the existence of the Secret du Roi—a system of private diplomacy conducted by King Louis XV. Unbeknownst to his foreign minister, Louis had established a network of agents throughout Europe with the goal of pursuing personal political objectives that were often at odds with France's publicly stated policies. Louis's goals for le Secret du roi included the Polish crown for his kinsman Louis François de Bourbon, Prince of Conti, and the maintenance of Poland, Sweden, and the Ottoman Empire as French allies in opposition to Russian and Austrian interests.