established their power. The remainder of his reign saw Austria relinquish many of these fairly impressive gains, largely due to Charles's apprehensions at the imminent extinction of the House of Habsburg. Charles III: Succession and the Pragmatic Sanction (1713–1740) For Charles now had succession problems of his own, having only two surviving daughters. His solution was to abolish sole male inheritance by means of the Pragmatic Sanction of 1713. In 1703 his father Leopold VI had made a pact with his sons that allowed for female inheritance but was vague on details, and left room for uncertainty. The Pragmatic Sanction strengthened this and in addition made provision for the inseparability (indivisibiliter ac inseparabiliter) of the Habsburg lands. This was to form the legal basis for the union with Hungary and to legitimise the Habsburg monarchy. It would be confirmed by the Austro-Hungarian Compromise of 1867 and would last to 1918. He then needed to strengthen the arrangement by negotiating with surrounding states. Internal negotiation proved to be relatively simple and it became law by 1723. Charles was now willing to offer concrete advantages in territory and authority in exchange for other powers' worthless recognitions of the Pragmatic Sanction that made his daughter Maria Theresa his heir. Equally challenging was the question of the heir apparent's marital prospects and how they might influence the European balance of power. The eventual choice of Francis Stephen of Lorraine in 1736 proved unpopular with the other powers, particularly France. War continued to be part of European life in the early 18th century. Austria was involved in the War of the Quadruple Alliance and the resulting 1720 Treaty of The Hague was to see the Habsburg lands reach their greatest territorial expansion. War with France had broken out again in 1733 with the War of the Polish Succession whose settlement at the Treaty of Vienna in 1738 saw Austria cede Naples and Sicily to the Spanish Infante Don Carlos in exchange for the tiny Duchy of Parma and Spain and France's adherence to the Pragmatic Sanction. The later years of Charles's reign also saw further wars against the Turks, beginning with a successful skirmish in 1716–1718, culminating in the Treaty of Passarowitz. Less successful was the war of 1737–1739 which resulted in the Austrian loss of Belgrade and other border territories at the Treaty of Belgrade. On the domestic front military and political gains were