A 28-year-old queen inherited a throne, and most of Europe decided to fight over it

When Maria Theresa inherited the Habsburg domains in 1740, Frederick the Great of Prussia immediately invaded her wealthy province of Silesia, testing whether other powers would honor the treaty guaranteeing her succession. They didn't: France, Bavaria, Spain and Saxony piled in against her, while Britain backed Austria, dragging the fighting into North America and India. The 1748 Treaty of Aix-la-Chapelle ended the war largely where it started, except Austria ceded Silesia to Prussia.

— Wikipedia contributors, War of the Austrian Succession — 1740–1748