premise: Maria Theresa reigned for only one year.
hypothesis: Maria Theresa Walburga Amalia Christina ( Maria Theresia [ maˈʁiːa teˈʁeːzi̯a ] 13 May 1717 -- 29 November 1780 ) was the only female ruler of the Habsburg dominions and the last of the House of Habsburg . She started her 40-year reign when her father , Emperor Charles VI , died in October 1740 . Frederick II of Prussia ( who became Maria Theresa 's greatest enemy for most of her reign ) promptly invaded and took the affluent Habsburg province of Silesia in the nine-year conflict known as the War of the Austrian Succession .