After the war, Italy failed to annex Dalmatia (which had been promised by Britain and France in the Treaty of London to induce Italy to join the war), and had to fight some more years to annex the city of Fiume, which had an Italian population, and this led several Italian politicians to speak of a "mutilated victory".
Indeed, it should not have been difficult to see how, among the Allied Powers, Italy had been the one which benefited the most from the outcome of the war. Whereas Britain and France still faced a Germany which had kept about 80 percent of her industrial and economic potential and thus could attempt a revanche in a matter of years, Italy had definitively gotten rid of her century-old enemy: instead of the Austro-Hungarian Empire there were now a number of smaller states, none of which could pose a credible threat, and some of them could even fall within the Italian sphere of influence.
With the annexation of Trento, Triest, South Tyrol, Friuli, Istria, Zara and some Dalmatian islands, Italy had completed her territorial expansion and could now rely on secure borders. Furthermore, Italian sovereignty over Rhodes and the Dodecanese had been officially recognized, as well as the Italian special interests in Albania. However, a Yugoslavian state was created in order to limit Italian influence and expansion on the Balkans, and thus Italy was quite isolated. The Italian politicians failed to perceive the positive elements of the peace treaties and stressed the negative ones, and so the myth of the "mutilated victory" spread, fueling the Fascist propaganda and helping Mussolini seize power.
During the war, Italy had suffered fewer casualties than Britain and much fewer than France, and the social problems she was facing afterward (an inflated war industry to reconvert to civilian production, the large number of crippled people no longer able to sustain themselves, the new role of women) were common to other Allied countries which, however, did not suffer an authoritarian drift. The difference between Italy and the other western allies lies in the more arbitrated economic and social conditions, which made it more difficult for Italy to recover from similar difficulties. Due to similar reasons, most south and east European countries had to face political unrest, dictatorship and fascism in the period between the World Wars.