On the 23rd May, 1915 the Kingdom of Italy declared war to the Austro-Hungarian Empire. Following its withdrawal from the Triple Alliance, Italy joined the powers of the Triple Entente. In case of victory, Italy was ensured in exchange the territories of Trentino, Istria, and part of Dalmatia. The Austro-Hungarian Army, already engaged in warfare since August 1914 on the Serbian and Galicia fronts, had prepared a defensive line from Stelvio to the Adriatic sea.

With the declaration of war by Italy, Cortina d'Ampezzo - that had belonged to the Hapsburgs since 1511 - was abandoned by the Austrian Army which retreated to a fortified line of resistance dating from the end of 1800, with strongholds at the Tre Sassi Fort on the Valparola Pass.

The Italian Army occupied Cortina on the 29th May, thus interrupting four centuries of rule by the Hapsburg Empire. The advance towards Val Badia and Val Pusteria, was slow and cautious; the Austrian defensive line of the Valparola Pass was reached only on the 15th June.