This was not the demography of stability.

From The Long Shadow: The Legacies of the Great War in the Twentieth Century by David Reynolds.  Page 14.

The new states of central and eastern Europe had been able to emerge because of the vacuum created by the collapse of German and Russian power. But as those two countries revived in the 1920s and 1930s, they resumed their struggle for territory and influence, with Poland, Ukraine, and the Baltic states again the battleground. Although Russo-German antagonism ignited eastern Europe’s next war in 1941, its fuel was the ethnic animosities of the post-imperial era—the disputed borders and oppressed minorities. Consider some simple demographic statistics from 1930. In Poland, 65 percent of the population were Poles, 16 percent Ukrainian, and 10 percent Jews. Czechs constituted only 51 percent of the people of Czechoslovakia; 23 percent were German and 16 percent Slovak. In Yugoslavia the ruling Serbs (44 percent) were not even a majority, 30 percent of the population being Croats and 9 percent Slovenes. This was not the demography of stability.