The so called "League of Fiume" - also known as "League of the oppressed peoples" - was intended to be a sort of answer to Wilson's League of Nations. Wilson's racism was well known, before, during and after the war, to the point where the Italians felt confident calling him out on it even after the "pacification" of Libya and the conquest of Ethiopia. Of course, looking from a distance, Aldrovandi-Marescotti's retelling of the minor incident between S. Sonnino and Edith Wilson at a dinner table, in 1937-38, sounds quite tone deaf and less than genuine.

The First Lady had apparently remarked, audibly, that those setting up the tables had set up together "people who don't agree with each other" - to which Sonnino, who was sitting at the same table, had, quite audibly, added "indeed".

Well, it may be that it's somewhat easier to sympathize for the oppressed when you feel you are being oppressed as well; but the issue of racial discrimination in the US wasn't, quite understandably, of prominent importance for Italian populists, politicians, establishment, or people by and large. Exceptions existed - and, indeed the American Civil War had been of significant interest for the Italians (despite them being in the middle of their own unification process), both because of the traditional sympathy for the Great American Republic (also, curiously, often referred to as the "Great American Confederation"), somewhat common even outside of Republicans properly speaking, for a natural contempt for the abhorrent institution of slavery, and because of the dramatic fluctuations in the prices of cotton and grain exports.

If you examine contemporary Italian press - not that I have examined everything, to be fair, and I am also not an expert on Italian "American studies" of late XIX and early XX Century - you'll find that, not only those kind of racial issues are limited to minor polemical quips, but that the general imprint is not exactly favorable to those we'd nowadays describe as "people of color". This, in good measure, because of the mixed "ethnical" character of the French occupation forces, which had been subject of frequent episodes of tension with the Italians - notably in Fiume, where a certain number of "Annamites" had been killed in incidents with Italian mariners and soldiers on July 6^th 1919. The timing of D'Annunzio's coup had been driven in good part by the deliberation of the inter-Allied committee which had demanded the withdrawal of most of the Italian occupation forces from the city, as well as of the remaining "Annamites", in consequence of those incidents.

Even when sympathy was expressed - and one should not dismiss entirely D'Annunzio's desire to appeal to oppressed minorities - certain priorities are difficult to rationalize from a modern perspective. So, for instance, in his infamous speech of late May 1919, D'Annunzio's most incendiary remark against Wilson apparently concerned the aforementioned Edith and her supposed proclivity for Slavic types...

Now, there isn't a very large body of literature on the "League of Fiume" - which has inspired one of the most dedicated (and "peculiar") students of Fiume, Micheal Leeden, to call for an increased focus on it - but, for the most part, that's because the whole concept of the "League" failed to result into anything of substance. Indeed its main proponent, the poet and musician Léon Kochnitzky, not only resigned from his position as "Head of Foreign Relations" (which he had taken up in January 1920) before the "League" could be officially inaugurated - on the first anniversary of D'Annunzio's proclamation in September 1920 - but indeed (on April 19^th 1920) even before the Command of Fiume acknowledged that such a project existed in a public statement released on April 28^th 1920.

Up to that point, the main focus of Fiume's "Foreign Office" had been to secure a degree of collaboration with the Irish - who had a much, much greater political and economical weight behind them, and very little desire to squander it losing the sympathies of the Vatican and risking antagonizing the US Government (and indeed chose to decline D'Annunzio's advances). Other attempts had been made with the Egyptians - who were in the midst of a process of international definition of their protectorate status (which the Italians believed Lord Curzon held quite dear), and rapidly lost most of their confidence in the Italian project when a promised delivery of 250,000 rifles fell through, or, more properly, never really started, as I don't think they had that amount of materials at hand. Of course, in the Egyptian matters, it's certainly true that the Italian Foreign Office (which, unlike the one based in Fiume could spare a few guns), had taken an interest in the matter, as Italy was still busy with the persistent insurrection of the "Senussi tribes" which often operated across the Libyan-Egyptian border (on this point especially, besides Leeden's earlier works, see Tedeschini-Lalli, M. - La questione Araba e la Lega dei Popoli Oppressi nella Fiume D'Annunziana). The Italian Foreign Office had also learned of the initiative a few weeks before D'Annunzio's first official statement (at least in March 1920, according to Leeden's D'Annunzio a Fiume), which is understandable, since communications in and from Fiume were usually controlled and the Italians, if they were willing to cautiously meddle with the Eastern Mediterranean affairs of the British, would not wish to touch, even indirectly or by accident, the Irish question.

As you can see, in Fiume, idealistic and often fantastic, radical ideas, tended to grow entangled with the most basic, practical and, at times, base interest of low end international politics. So, if Kochnitzky - on March 22^nd 1919 - had called for "collecting together all the scattered forces of the oppressed":

peoples, nations, races [...] and by these means to be able to fight back and defeat the overbearing imperialistic organisms (such as the British Empire for instance)

D'Annunzio's statement of April 28^th 1919, mentioned the "explicit adhesion" of Ireland and Egypt as well as

of the whole of Islam, and of the peoples committed to fight against the barbaric Serbian domination: Croats, Montenegrins, Albanians, Bulgaro-Macedonians

A statement where someone might recognize a hint of Giovanni Giuriati, Head of Cabinet in Fiume, and influential figure in the Italian war-propaganda office, at the time industriously committed to infiltrate Radic's autonomist Croatian "Peasant Party".

It is in the aforementioned, private, letter from Kochnitzky to D'Annunzio of March 22^nd (as reproduced in De Felice, R. - La Carta del Carnaro), that you find the reference to the “oppressed races”, especially to those you mention. As a whole, Kochnitzky aspired to form an organism inclusive of representatives from:

Oppressed peoples: Fiume d'Italia, Dalmatian Isles, Albania, German Austria, Monenegro, Croatia, German Irredenti [the Germans outside of the national borders] now subject to Poland, to Czechoslovakia, to France, to Italy (reservation, autonomy) and to the pseudo-League of Nations, Catalans, Maltese, Gibraltar, Ireland, Flemish

Islam, Morocco, Algeria, Tunisia, Egypt, Libya, Syria, Palestine, Mesopotamia, India, Persia, Afghanistan. India [Indochina], Birmania [Burma], China, Korea, Philippine Islands, Hawaii, Panama, Cuba, Puerto Rico.

Oppressed Races: Chinese of California, Negroes of America, Israelite problem.

Countries treated unfairly in Versailles: Russia, Romania, Belgium, Portugal, Siam, Germany, Hungary, Bulgaria, Turkey and the Holy See

Delegations of groups and parties in solidarity with Fiumanesimo, especially Italian, French, British and American.