Most of the region was included from the 11th cent. to 1802–3 in the episcopal principalities of Trent and Bressanone. In 1815 it was put under direct Austrian administration and incorporated into the Tyrol. After Trento passed to Italy in 1866, the Austrians pressed for increased Germanization in Bolzano. This led to irredentism among the Italian minority there. After World War I, the Treaty of Saint-Germain (1919) gave Bolzano to Italy, which resulted in agitation by its German-speaking population.
The Italian Fascist government's program of intensive Italianization and the enforcement of Italian as the sole official language met with violent opposition. An agreement in 1938 between Hitler and Mussolini provided for extensive forced migration of the German-speaking population to Germany or to other parts of Italy. However, this program was extremely unpopular and soon collapsed. Following an agreement (1946) between the Italian and Austrian governments, the republican constitution of Italy (1947) granted the region considerable autonomy. Both German and Italian were made official languages, and German schools were permitted in Bolzano province. However, the German-speaking population in the province (called Südtirol, or South Tyrol, by the Germans) continued to demand greater autonomy. They received the backing of Austria, which charged that the German-speaking population in Bolzano had not been given the autonomy envisaged in the 1946 Austro-Italian agreement.
Serious tension developed between the two countries. In 1960 the Bolzano problem was debated, at Austria's request, at the United Nations, on whose recommendation Italy and Austria entered into direct negotiations. Their efforts were partially vitiated by acts of terror committed in the region in 1961. It was only in 1971 that a treaty was signed and ratified; this agreement stipulated that disputes in Bolzano would be submitted for settlement to the International Court of Justice in The Hague, that the province would receive increased legislative and administrative autonomy from Italy, and that Austria would not interfere in Bolzano's internal affairs. The region was granted increased autonomy in 1972.