Assuming that political history goes roughly like OTL - Austroslavism can be a viable political ideology ITTL, and Austro-Hungary would be much more stable (If Hungarian speak Slavic, it means that Croatian and Slovakian national consciousness never arise - they're catholic Slavs just like alt-Hungarians). After IWW, there are a chances to form Western Slavic union out of Bohemia, Hungary and Poland (Polish-Hungarian friendship is strong and ITTL Dmowski and Endecja would suport such a union to stop German expansion) instead of OTL Czechoslovakia. It may even have a form of monarchy with either Karl Habsburg (he was quite popular in Poland and there was even a plan IOTL to make him king of Poland) or some Romanov/Windsor (Karel Kramar wanted to create Western Slavic Federation with Romanov in charge IOTL and Windsor is well-connected and could be seen by local politicians as a pawn). On the other hand Yugoslavia would never arise - yugoslavism was propagated by Croat nationalists who felt oppresed by foreign Hungarians. ITTL, Croats and Hungarians are the same nation - with Hungary-Croatia union happening in early Medieval perion and closeness in language, Croats would become a special variation of Hungarians - just like Bavarians are exceptional example of German, but still German nonetheless. In this case, Italy and Serbia would divide Dalmatia and Serbia would take Bosnia. If Italy gains additional land in Dalmatia it might also butterfly Mussolini (but this is not a given) and probably such Western Slavic union could be powerful enough to push Bolsheviks further east and to gain more lands from Germany. It could even lead to division of Russia as a result of RCW - Czech would push for helping Whites, Hungarians would be neutral and Poles would obviously want gains in Eastern Borderlands, but even WSF wouldn't be enough to completely oust Bolsheviks from power.
@Jan Olbracht
