Why did the Soviet Union and Yugoslavia disintegrate?

The disintegration of the Soviet Union and Yugoslavia: It was because of SB’s ethnic policy, which suppressed the Russians, the dominant ethnic group, and emphasized the characteristics of each ethnic minority, instead of integrating into the dominant ethnic group like the United States. Otherwise, even if it fails, like Poland and other former communist countries in Eastern Europe, it will just be ruled by people from other parties, and the country will not disintegrate. ? Who will be the third major disintegrating country?