qnli question: What year did the Kingdom of Prussia become the leading state of the German Empire? sentence: Following Nazi Germany's defeat in World War II in 1945, war-torn East Prussia was divided at Joseph Stalin's insistence between the Soviet Union (the Kaliningrad Oblast in the Russian SFSR and the constituent counties of the Klaipėda Region in the Lithuanian SSR) and the People's Republic of Poland (the Warmian-Masurian Voivodeship).