Pope Pius XII was head of the Catholic Church and sovereign of the Vatican City State from 2 March 1939 until his death in October 1958. Before his election to the papacy, he served as secretary of the Department of Extraordinary Ecclesiastical Affairs, papal nuncio to Germany, and Cardinal Secretary of State, in which capacity he worked to conclude treaties with various European and Latin American nations, including the Reichskonkordat treaty with the German Reich.

Vatican City, officially the Vatican City State, is a landlocked sovereign country, city-state, microstate, and enclave within Rome, Italy. It became independent from Italy in 1929 with the Lateran Treaty, and it is a distinct territory under "full ownership, exclusive dominion, and sovereign authority and jurisdiction" of the Holy See, itself a sovereign entity under international law, which maintains the city-state's temporal power and governance, diplomatic, and spiritual independence. The Vatican is also a metonym for the pope, Holy See, and Roman Curia.