I want to know the answer to the following question:
Why were the prince electors able to proclaim themselves King of Prussia?
All the background I'm provided with is that "After the annexation of most of western Royal Prussia in the First Partition of the Polish-Lithuanian Commonwealth in 1772, eastern (ducal) Prussia was connected by land with the rest of the Prussian state and was reorganized as a province the following year (1773).". Is that enough to answer the question?