 In December , King Frederick II of Prussia invaded the Duchy of Silesia and requested that Maria Theresa cede it , threatening to join her enemies if she refused . Maria Theresa decided to fight for the mineral @-@ rich province . Frederick even offered a compromise : he would defend Maria Theresa 's rights if she agreed to cede him at least a part of Silesia . Francis Stephen was inclined to consider such an arrangement , but the Queen and her advisers were not , fearing that any violation of the Pragmatic Sanction would invalidate the entire document . Maria Theresa 's firmness soon assured Francis Stephen that they should fight for Silesia and she was confident that she would retain " the jewel of the House of Austria " . The invasion of Silesia by Frederick was the start of a lifelong enmity ; she referred to him as " that evil man " . 
