structural:reformatting
Foreign relations – New alliances; the War of the Polish Succession

In the first years of his governance, Fleury and his foreign minister Germain Louis Chauvelin sought to maintain the peace by maintaining the French alliance with Great Britain, despite their colonial rivalry in North America and the West Indies. They also rebuilt the alliance with Spain, which had been shaken by the anger of the Spanish King when Louis refused to marry the Spanish infanta. The birth of the king's male heir in 1729 dispelled the risks of a succession crisis in France. However, new powers were emerging on the European stage, particularly Russia under Peter the Great and his successor, Catherine. The Habsburg monarchy under Charles VI was assembling a scattered but impressive empire as far as Serbia in southeastern Europe with territories taken from the Ottoman Empire, and from Spain, acquiring the Austrian Netherlands, Milan and the Kingdom of Naples.

A new coalition against France began to assemble in eastern Europe, sealed by a defensive treaty signed on 6 August 1726 between Prussia, Russia and Austria. In 1732 the coalition came into direct conflict with France over the succession to the Polish throne. The King of Poland and Elector of Saxony, Augustus II, was dying, and the favoured candidate to succeed him was Stanislaus I Leszczyński, the father of the Queen of France. In the same year Russia, Prussia and Austria signed a secret agreement to exclude Stanislaus from the throne, and put forward another candidate, Augustus III, son of the deceased Polish king. The death of Augustus on 1 February 1733, with two heirs claiming the throne, sparked the War of the Polish Succession. Stanislaus traveled to Warsaw, where he was elected and crowned on 12 September. Empress Anna of Russia immediately marched her regiments into Poland to support her candidate. Stanislaus was forced to flee to the fortified port of Danzig, while on 5 October Augustus III was crowned in Warsaw.

Cardinal Fleury responded with a carefully orchestrated campaign of diplomacy. He first won assurances from Britain and Holland that they would not interfere in the war, while lining up alliances with Spain and Charles Emmanuel III of Sardinia in exchange for pieces of the Habsburg monarchy. On 10 October 1733, Louis formally declared war against Austria. A French army occupied the Duchy of Lorraine, while another crossed the Alps and captured Milan on 3 November, handing it over to the King of Sardinia. Fleury was less energetic in his actions to restore the Polish throne to Stanislaus, who was blockaded by the Russian navy and army in Danzig. Instead of sending the largest part of the French fleet from its station off Copenhagen to Danzig, he ordered it to return to Brest and sent only a small squadron with two thousand soldiers, which after a fierce action was sunk by the Russians. On 3 July Stanislaus was forced to flee again, in disguise, to Prussia, where he became the guest of King Frederick William I of Prussia in the castle of Königsberg.

To bring the war to an end, Fleury and Charles VI negotiated an ingenious diplomatic solution. Francis III, Duke of Lorraine, left Lorraine for Vienna, where he married Maria Theresa, the heir presumptive to the Habsburg thrones. The vacant throne of Lorraine was to be occupied by Stanislaus, who abandoned his claim to the Polish throne. Upon the death of Stanislaus, the Duchy of Lorraine and Bar would become part of France. Francis, as the future emperor, would be compensated for the loss of Lorraine by the granting of the Grand Duchy of Tuscany. The King of Sardinia would be compensated with certain territories in Lombardy. The marriage of Francis of Lorraine and Maria Theresa took place in 1736, and the other exchanges took place in turn. With the death of Stanislaus in 1766, Lorraine and the neighboring Duchy of Bar became part of France.

In September 1739, Fleury scored another diplomatic success. France's mediation in the war between the Holy Roman Empire and the Ottoman Empire led to the Treaty of Belgrade (September 1739), which favoured the Ottoman Empire, beneficiary of a Franco-Ottoman alliance against the Habsburgs since the early 16th century. As a result, the Ottoman Empire in 1740 renewed the French capitulations, which marked the supremacy of French trade in the Middle East. With these successes, Louis XV's prestige reached its highest point. In 1740 Frederick William I of Prussia declared "Since the Treaty of Vienna France is the arbiter of Europe."