Most of the people who had emigrated returned to the area in 1945. Despite Austrian efforts, South Tyrol remained part of Italy after World War II, and many chose to take up Italian citizenship after the Gruber–De Gasperi Agreement of September 1946. It was named after the foreign minister of Austria (Karl Gruber) and the prime minister of Italy (Alcide De Gasperi) and agreed on Trentino-Alto Adige/Südtirol to remain part of Italy ensuring its autonomy. Those who returned had to register both themselves and their children, and they had to prove, by means of a birth certificate, that they had the right to Italian citizenship.