Why did italy resent foreign powers after the treaty of versailles?

Vittorio Orlando was the prime minister of Italy. Italy had declared war on Germany in 1915 after the Secret Treaty of London. In the treaty France and Britain had agreed that Italy would be given the Adriatic coast at the end of the war. When Orlando arrived at Versailles he expected Britain and France to keep to their word.
Italy was given the two small areas of Istria and the South Tirol. The Adriatic coast was made part of a new country called Yugoslavia, which included Serbia and Bosnia.
Italy did not receive the land of the Adriatic coast that they were promised.