Why was Vatican City created as an independent state under the pope?

Vatican City was established as an independent state in 1929 through the Lateran Treaty to resolve the "Roman question," a long-standing dispute between the papacy and the Italian state.12

Following the unification of Italy and the seizure of the Papal States in 1870, the pope lost his temporal territories and refused to recognize the new Italian government, effectively becoming a voluntary "prisoner of the Vatican" for nearly 60 years. The 1929 treaty ended this conflict by granting the Holy See full sovereignty over a small, defined territory.345

The primary purpose of creating this independent state was to ensure the pope’s autonomy, allowing him to exercise his universal authority as the head of the Roman Catholic Church without being subject to the political influence or control of any other nation. By securing this independence, the treaty also helped subside the tensions between the church and the Italian state that had been fueled by anticlericalism and the loss of papal lands.342