Succession to the Habsburg dominions
When Charles succeeded his brother in 1711, he was the last male Habsburg heir in the direct line. Since Habsburg possessions were subject to Salic law, barring women from inheriting in their own right, his own lack of a male heir meant they would be divided on his death. The Pragmatic Sanction of 19 April 1713 abolished male-only succession in all Habsburg realms and declared their lands indivisible, although the Diet of Hungary only approved it in 1723.
Charles had three daughters, Maria Theresa (1717–1780), Maria Anna (1718–1744) and Maria Amalia (1724–1730), but no surviving sons. When Maria Theresa was born, he disinherited his nieces, who were the daughters of his elder brother Joseph I, Maria Josepha and Maria Amalia. It was this act that undermined the chances of a smooth succession as set out in a Pact arranged by his father, and obliged Charles to spend the rest of his reign seeking to ensure enforcement of the sanction from other European powers.
Charles agreed to a demand from Britain that he close a trading company, the Ostend Company, which was based in the Austrian Netherlands and which he himself had founded in 1722. Other signatories included Britain, France, the Dutch Republic, Spain, Russia, Denmark-Norway and Savoy-Sardinia, but subsequent events underlined Prince Eugene of Savoy's comment that the best guarantee was a powerful army and full treasury. Charles's nieces were married to the rulers of Saxony and Bavaria, both of whom ultimately refused to be bound by the decision of the Imperial Diet. France, despite publicly agreeing to the Pragmatic Sanction in 1735, signed a secret treaty with Bavaria in 1738 promising to back the "just claims" of Charles Albert of Bavaria.
In the first part of his reign, the Habsburg monarchy continued to expand thanks to the success in the Austro-Turkish War (1716–1718), adding Banat to Hungary and establishing direct Austrian rule over Serbia and Oltenia (Lesser Wallachia). This extended the Austrian rule to the lower Danube.
The War of the Quadruple Alliance (1718–1720) followed. It too ended in an Austrian victory; by the Treaty of The Hague (1720), Charles swapped Sardinia, which went to the Duke of Savoy, Victor Amadeus II, for Sicily, the largest island in the Mediterranean, which was harder to defend than Sardinia. The treaty also recognised Philip V of Spain's younger son, Don Carlos (the future Charles III of Spain) as heir to the Duchy of Parma and Grand Duchy of Tuscany; Charles had previously endorsed the succession of the incumbent Grand Duke's daughter, Anna Maria Luisa, Electress Palatine.
Peace in Europe was shattered by the War of the Polish Succession (1733–1738), a dispute over the throne of Poland between Augustus of Saxony, the previous king's elder son, and Stanisław Leszczyński. Austria supported the former, France the latter; thus, a war broke out. By the Treaty of Vienna (1738), Augustus ascended the throne, but Charles had to give the kingdoms of Naples and Sicily to Don Carlos in exchange for the much smaller Duchy of Parma and Grand Duchy of Tuscany.
The question of Charles's elder daughter's marriage was raised early in her childhood. She was first betrothed to Léopold Clément of Lorraine, who was supposed to come to Vienna and meet Maria Theresa. Instead, he died of smallpox in 1723, which upset Maria Theresa. Léopold Clément's younger brother, Francis Stephen, then came to Vienna to replace him. Charles considered other possibilities (such as Don Carlos) before announcing the engagement to Francis. At the end of the War of the Polish Succession, France demanded that Francis surrender the Duchy of Lorraine (his hereditary domain) to Stanisław Leszczyński, the deposed king of Poland, who would bequeath it to France at his death. Charles compelled Francis Stephen (duke of Lorraine of 1729-1737) to renounce his rights to Lorraine and told him: "No renunciation, no archduchess."
Charles had a number of sexual relationships with male courtiers, including his Master of the Horse, Prince Schwarzenberg, and a hunter's boy. The love of his life was Michael Joseph, Count Althann, a groom of the bedchamber, whom he called "my only heart, my comfort [...] my soul mate", and with whom he slept regularly. Althann's death in 1722, after a relationship of nineteen years, devastated him.
In 1737, the Emperor embarked on another Turkish War, in alliance with Russia. Its start was promising. Already in the autumn of the same year, imperial troops took Niš and tried to consolidate gains in 1738, but during the next year, Habsburg armies suffered several defeats. By the Treaty of Belgrade (1739), Emperor Charles had to cede several regions to the sultan, including the Bosnian section of Posavina, the central regions of Serbia, and Wallachia Minor (Oltenia). Popular discontent at the costly war reigned in Vienna; Francis of Lorraine, Maria Theresa's husband, was dubbed a French spy by the Viennese.
