 It was only on April 26, 1915 that the latter nation declared war on the Central Powers.This change in attitude is attributed by historians to the secretive signing of the Treaty of London, which entailed that in exchange for Italy's support the country ""shall obtain the Trentino, Cisalpine Tyrol with its geographical and natural frontier (the Brenner frontier)"" from the German-aligned Austro-Hungarian Empire.Despite petitions from public officials in South Tyrol and reassurances from United States President Woodrow Wilson that the "readjustment of the frontiers of Italy should be effected along clearly recognizable lines of nationality," southern Tyrol and Trentino fell under Italian military administration with the signing of the Treaty of Saint-Germain-en-Laye in September 1919.