Italy became a republic after a referendum held on 2 June 1946, a day celebrated since as Republic Day. This was the first time that Italian women voted at national level, and the second time overall considering the local elections that were held a few months earlier in some cities. Victor Emmanuel III's son, Umberto II, was forced to abdicate and exiled. The Republican Constitution was approved on 1 January 1948. Under the Treaty of Peace with Italy, 1947, Istria, Kvarner, most of the Julian March as well as the Dalmatian city of Zara was annexed by Yugoslavia causing the Istrian-Dalmatian exodus, which led to the emigration of between 230,000 and 350,000 of local ethnic Italians (Istrian Italians and Dalmatian Italians), the others being ethnic Slovenians, ethnic Croatians, and ethnic Istro-Romanians, choosing to maintain Italian citizenship. Later, the Free Territory of Trieste was divided between the two states. Italy also lost all of its colonial possessions, formally ending the Italian Empire. In 1950, Italian Somaliland was made a United Nations Trust Territory under Italian administration until 1 July 1960. The Italian border that applies today has existed since 1975, when Trieste was formally re-annexed to Italy.