Short answers, pulled from the story.
The Kingdom of Prussia was founded on the 18th of January 1701, when Frederick III crowned himself King in Prussia, and it ended in 1918 with the German Revolution. It was transformed into the Free State of Prussia and formally abolished in 1947.
The title 'King in Prussia' was a legal distinction acknowledging that the Hohenzollerns held royal authority only in the duchy of Prussia, which lay outside the Holy Roman Empire. Inside the empire, they remained electors subject to the emperor. Frederick only adopted the full title 'King of Prussia' in 1772, after annexing Royal Prussia in the First Partition of Poland.
Bismarck took office as Prussia's minister-president on the 23rd of September 1862 and guided Prussia through three wars: the Second War of Schleswig in 1864, the Austro-Prussian War of 1866, and the Franco-Prussian War of 1870-1871. These wars dissolved the German Confederation, created the North German Confederation under Prussian leadership, and culminated in the proclamation of the German Empire on the 18th of January 1871.
During the Seven Years' War (1756-1763), Prussia faced Austria, Russia, France, and Sweden simultaneously. The Russian army briefly occupied both Berlin and Konigsberg in October 1760. Prussia's survival was secured only when Empress Elizabeth of Russia died in 1762, an event called the Miracle of the House of Brandenburg, and her successor Peter III withdrew Russia from the war.
The Prussian three-class franchise, introduced in the Constitution of 1850, divided voters into three groups based on taxes paid and assigned each group equal electoral weight regardless of size. In a typical election, the top class representing 4% of voters chose the same number of electors as the bottom class representing 82%. The system guaranteed political dominance for the wealthy and landed Junker class while suppressing the political voice of the urban working and middle classes.
The imperial constitution explicitly tied the imperial crown to the Prussian crown, making it impossible to hold one without the other. When William II lost the support of the military and faced armed revolt in Berlin in November 1918, he had no legal mechanism to remain King of Prussia while abdicating as German Emperor. His abdication from both offices was announced on the 9th of November 1918.