Silesia was originally part of Austria, until the War of the Austrian Succession. When the king of Austria died without a male heir, he got almost everyone in Europe to sign the Pragmatic Sanction, which meant that they would recognize his daughter as the rightful ruler of Austria. When Frederick II became king of Prussia, he decided to ignore the document and invaded Silesia, which was one of the most important regions of Austria. It had excellent farming and natural resources, as well as a large population. Prussia managed to hold onto it through the ensuing war, which was called the War of the Austrian Succession.