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AFAIK the population of Czechoslovakia in the 1930s was about 15 million people. Of them about 10 million lived what is now the Czech Republic. Four million lived in Slovakia and one million in Ruthenia.
However, AFAIK 35% of the population of what is now the Czech Republic were German speakers and a quarter of the population of Slovakia spoke Hungarian as their first language.
With a POD of 1870 would it be feasible for the ratios of German to Czech and Hungarian to Slovak speakers to be more balanced? That is 45:55 in what is now the Czech Republic and 50:50 in what is now Slovakia.
If it was would that have been enough to prevent the creation of Czechoslovakia after World War One? That is what's now the Czech Republic would remain a part of Austria and Slovakia would remain part of Hungary. Ruthenia would be awarded to Poland whether the Ruthenians wanted to be or not.