The Treaty of Versailles at the end of World War I granted Italy a seat on the League of Nations, a share in German war reparations and control of the Tyrol region of the Austro-Hungarian Empire. Italy had expected much more, fueling resentment that would lead to the rise of fascism.
Italy had originally entered World War I on the side of the Allies as the result of the Treaty of London in 1915. This treaty promised an enormous amount of territory to Italy, including lands along its border with Austria-Hungary, islands in the Adriatic, portions of Albania and territory in the Ottoman Empire. When the war was over, Italy expected the treaty to be honored, but to do so would have interfered with the sovereignty of several groups in the region. The Allies were also disappointed with Italy's performance in the war, so they reduced the rewards Italy would receive. In response, the Italians pulled out of the treaty negotiations for a time, but ultimately accepted the terms offered.
The Treaty of Versailles was incredibly unpopular in Italy, and fueled significant anti-British, anti-French and anti-American sentiment in the country. Benito Mussolini later capitalized on this anger during his rise to power, and Italy's perceived mistreatment was one of the reasons he cited for Italy's entry into World War II on the side of Germany.