The accession of Charles to the imperial throne, deprived him of his support for allies in the War of Spanish Succession, which feared the union of Austria and Spain under a single scepter. This war raged for the legacy of the Spanish Habsburgs, after the death who was considered heir to the Spanish crown Bavarian Joseph Ferdinand of Wittelsbachs - son of the Austrian princess Maria Antonia. By the Treaty of Utrecht (1713) from the realms of the Spanish Hapsburg Emperor Charles were fixed for only the Spanish Netherlands and the Kingdom of Naples (soon lost as a result of the War of Polish Succession). Among the acquisitions of Italian emperors were the Duchy of Mantua and the island of Sardinia (which he in 1717 exchanged in Sicily).
In order to transfer their ancestral possessions daughters and their offspring Karl - strictly speaking, the last of the Hapsburgs - in 1713 adopted a law on succession, known as the Pragmatic Sanction. In 1736 he chose a husband of Maria Theresa, her eldest daughter and heiress, teshenskogo Duke Franz Stephan of Lorraine old. Despite the measures taken by the Emperor Charles to ensure international recognition of the Pragmatic Sanction, after his death, war broke out of the Austrian Succession, in which Maria Theresa and Franz Stefan managed to defend all the Habsburg possessions, except for parts of Silesia and the recently passed to him the Italian Duchy of Parma and Piacenza. After the election of the Emperor Franz in the Holy Roman Empire reigned Lorraine dynasty, to retain the name of the Habsburgs.