The Vittoria Mutilata and Germany's stab-in-the-back myth both have similarities in that they contributed to the rise of both the Italian Fascists and the German NSDAP, but both myths are different as to who was the scapegoat targeted, with Italian fascists and other right-wing groups blaming outside forces primarily, and the NSDAP blaming internal forces for its woes.

The Mutilated Victory myth seemingly makes sense on its surface level. The Entente powers promised Italy all its territorial claims on Austria-Hungary; including Istria, Trentino, South Tyrol, and Dalmatia, and other lands along the Adriatic coastline through the Treaty of London in 1915. When the peace was signed, only Istria, Trentino, and South Tyrol were awarded to Italy, with Fiume and a small toehold in Zara later being annexed in the months following. The remaining territories promised were awarded to the newly formed Kingdom of Yugoslavia.

The Italian delegation initially walked out of the talks after realizing that not all the territories promised under the Treaty of London would be awarded, but came back to the table shortly after to continue the post-war talks. The Italian delegation conceded to retracting their claims to Dalmatia and the Adriatic coast, which pleased the generals of the Italian army, who voiced displeasure at the idea of holding of a thin line of territory stretched along the Adriatic.

Many members of Italian society, however, saw this retraction in a much more negative light, most notable of which was Gabriele D'Annunzio who wrote scathing articles against Prime Minister Vittorio Emanuele Orlando for conceding so much territory in a war in which they were the victors.

What the Fascist intrepretation often omits is just that, that Italian delegates retracted the claim for practical reasons regarding defense, and instead reinterpret it as Britain and France strongarming Italy to deny the country land that should rightfully have been awarded to her. The narrative changed to suit Fascist political aims, that Britain and France are responsible for keeping Italy from realizing its full potential and that it's up to Italy itself to achieve her ambitions...and so on.

u/Klesk_vs_Xaero also does a wonderful writeup on the Mutiliated Victory and does it so much more justice than I ever could. I implore you to check that out as well.

Now lets get to Germany, where the antesemitic origins of the stab-in-the-back myth shows its face before the war even ended.

In October of 1916, the German Army ordered the Judenzählung, or Jewish Census, to address growing claims among the military and civilians that Jews are lacking in patriotic support for the German cause. The census disproved the accusations, citing over 100,000 German Jews serving in the Army, over 12,000 wounded, and over 35,000 decorated for valor on the battlefield, but the results were not made public.

The myth came fully into being in November of 1919, with General Erich Ludendorff claiming that his Germany's home front betrayed the Army at the end of the war, vehemently defending the notion that his army could continue to fight on, despite the reality that the German Army was completely exhausted in the closing weeks of the war.

Scapegoats listed by German right-wing parties jumped from group to group, blaming the civilians themselves, the Mutineers at Kiel, bankers who withheld/denied loans to the government due to concerns of imminent defeat, and finally the German Jewish population, which the NSDAP spent much effort on propaganda films and papers citing them as the primary source of betrayal within Germany.

As we can see, both myths served a similar purpose in contributing to the rise of authoritarian regimes in Italy and Germany, who propagated both narratives of betrayal as a foundation for their aggressive foreign policies. The main differences being who was the target to blame, with Italian Fascists blaming the other Allied Powers, and Germany blaming their own home front for their woes. As for the validity of both, both the Mutilated Victory and the Stab-in-the-back myth are just that, myths.

Sources

The Legend of the Mutilated Victory: Italy, the Great War, and the Paris Peace Conference, 1915-1919 by H. James Burgwyn

The Culture of Defeat: On National Trauma, Mourning, and Recovery by Wolfgang Schivelbusch

I have spent some time writing about this one - and now I don't have time to answer you properly!

I'll provide a very short summary of the main facts and defer to a substantial amount of poorly edited stuff I have put together - intro 1 - intro 2 - general observations - diplomatic concepts 1 - diplomatic concepts 2 - statistics - on the way to Paris - on the way back - reactions - the Allies - more reactions - Mussolini - political crisis - diplomatic crisis - complaints - more details - and more - for those who want more.

This is unfortunately a topic where being concise works much to the detriment of understanding. If you have follow up questions, I'll do my best to address them as soon as I have time. Notably though, I am not an expert on the "stab in the back" myth, and can't therefore develop exact analogies, outside of the broadly apparent similarities.

Italy had entered the Great War at the end of a laborious negotiation predicated on the completion of her national unity (with the addition of Trento and Trieste) and on the establishment of here security in the Adriatic sea (with the acquisition of a predominant position on the strategically stronger eastern coast).

The results of the Treaty of St. Germain clearly accomplished the first point (it is true that a certain amount of Italians remained outside of the new border, but no substantial Italian majority was left and rather a few regions were included for strategic reasons, such as south Tyrol, where the Italians were a minority). As for the second, one can also clearly see how such an aspiration could clash with the new ideas exposed by Wilson in his fourteen points and largely accepted, at least "in principle", by the Allied Powers.

The American opposition to the Italian claims over Dalmatia and the easternmost portion of the eastern coast of Istria (roughly from p.ta Fianona) was the main obstacle to the accomplishment of the second Italian aspiration.

On purely practical grounds - given the explicit opposition of the Associated and the (understandable) reluctance of the Allies to take steps contrary to Wilson's intention on the matter - the Italian delegation could have assumed a more reasonable position and accepted the impossibility of securing the whole amount they had aspired to.

They were prevented from doing so by a series of elements of internal character, partly resulting from the lasting tension of the war (the fracturing between neutralists and interventionists, concerns over the growing influence of "Bolshevism" on the Italian masses, the rise of nationalist themes) and partly caused by their own inclination to incite rather than control popular enthusiasms.

This was the case of Fiume - a port town, with a relatively sizable Italian majority in its center, and a largely Slav suburb (Sussak), making for a more or less equal split depending on where one set the border - formerly autonomous part of Croatia under special status granted by the Kingdom of Hungary. The National Council (which is the organism of the Italian urban majority) had demanded annexation to Italy at the end of October 1918 and had been received favorably by V.E. Orlando's government.

The main problem was that Fiume was not only apart from the rest of italy, with a good portion of "ethnically Slav" land in between, but outside of the demarcation line established with the Treaty of London, which - even worse - reserved it for the unspecified formation of "Croatia, Serbia and Montenegro" (the ambiguity was intended, as Croatia was at the time, the province of the Kingdom of Hungary).

For this reason, Sidney Sonnino - the Italian Foreign Minister who had worked to secure the compensations for the italian intervention, and who represented the continuity of the Italian struggle for the completion of the aforementioned two aspirations, and was therefore, despite his old-diplomacy approach, a "symbol" for the new nationalist forces against the democratic ideas of "Wilsonism" - was insistent that Fiume had to be abandoned and that Italy had to stick with the Treaty of London.

While his position lacked subtlety and was extremely rigid, it had the quality of being intrinsically coherent. On the other hand, Orlando - who had a more "democratic" inclination, but also a tendency to interpret those new principles in the most convenient way - chose to follow a more "fluid" approach: to demand Dalmatia in observance of the Treaty of London, and Fiume in observance of the principle of self-determination, only to then transact on portions of Dalmatia as a compensation for the assignation of Fiume.

Such a strategy required both an excellent diplomatic coordination (in reality, the Italian delegation was a mess, with Sonnino arguing with everyone else while the Italian Ambassador to the US had mistakenly informed them that Wilson was fairly open to the Italian demands) and a sizable amount of good will from the other powers (which, deservedly or not, was soon rather scarce).

This led to Orlando's failure in securing the city of Fiume (for now). In material terms it wasn't really a dramatic loss - much worse was the deterioration in the relations between Italy and her Allies, between Italy and the Yugoslavs, between Italy and herself.

The process of diplomatic crisis went on parallel to one of growing internal instability, the solution of which - according to Orlando - resided in appeasing the national forces. But his attempts in this direction (besides the diplomatic misfortunes) had the negative consequence of provoking a bout of activity by all those groups who had a direct investment with those forces - steelworks and shipbuilding companies, the Trieste based groups, which regarded Fiume as both a dangerous rival and a possible subsidiary, the Navy and the Army which, for different reasons, looked with concern at the opening of demobilization.

In extreme summary, the result of the unrest around Fiume was the creation of a state of persistent internal struggle and fragmentation which became visible in certain ordinary manifestations of the state's action - and of which D'Annunzio's occupation of the city with the help of army regiments and a few favorable outlooks from the army leaders, was only the most apparent and revealing sign.

The entire affair became a monkey wrench into the machinery which was to bring the country back to normalcy - and even when the system was able to shake off the matter of Fiume with the Treaty of Rapallo of 1920 and the dislodgement of D'Annunzio's legionnaires from the city, it wasn't able to reset itself entirely.

Of course, the Fascist narrative of these events is the complete opposite of the one I provided. Adopting the nationalist platform, the Italian aspirations were not only fully justified, but already very, very modest in nature - and failing to accomplish them was a symptom of the inability of the liberal system which, even if led by well meaning figures like Orlando and Sonnino, could not secure the prize earned by the Italian people. There was a deep disconnect between the true, positive, new forces of the nation, unleashed during the war and expressed in the colossal victory which had smashed the Austro-Hungarian Army and the old, crumbling, inept liberal state. If the Great War had been the culmination of the Italian Risorgimento, it had also proved the limits of the state produced by the Italian unification - hence the need for the true culmination of the Italian resurgence: the Fascist revolution.

In this narrative, D'Annunzio's special distinction came from having been the first to point out this disconnect - between those who had won the victory and those, inside and outside of Italy, who threatened to mutilate it. From foreseeing (the expression was first written down in one of D'Annunzio's songs composed to celebrate the last Italian offensive, several weeks before the general disillusionment sparked by Wilson's message) that the true forces of the Italian nation had to keep up the victorious fight, in an endless struggle to secure Victory from her mortal enemies.