Upon succeeding to the throne on 31 May 1740, and desiring the prosperous Austrian province of Silesia (to which Prussia had a minor claim), Frederick declined to endorse the Pragmatic Sanction of 1713, a legal mechanism to ensure the inheritance of the Habsburg domains by Maria Theresa of Austria, daughter of Holy Roman Emperor Charles VI. Thus, upon the death of Charles VI on 29 October 1740, Frederick disputed the succession of the 23-year-old Maria Theresa to the Habsburg lands, while simultaneously making his own claim on Silesia. Accordingly, the First Silesian War (1740–1742, part of the War of the Austrian Succession) began on 16 December 1740 when Frederick invaded and quickly occupied the province. Frederick was worried that if he did not move, Augustus III, King of Poland and Elector of Saxony, would seek to connect his own disparate lands through Silesia. The Prussian king quickly snatched the territory, using as justification an obscure treaty from 1537 between the Hohenzollern and the Piast dynasty of Brieg (Brzeg).