There are several factors that produce stability of the multinational societies and many other that cause instability. With this work the attempt is to examine the possibilities of successful accommodation and keep the unity and stability of the country. The main three aspects that the analysis includes are: political autonomy and institutionalization of separate jurisdictions within which minorities (national groups) enjoy extensive devolved powers of self-government; power-sharing that includes representatives of minorities in the governing of the larger state; principle of inclusiveness that allows all members of a self-governing groups to accede to the state-wide political process Multinational federations with self-governing constituent units, usually combine mainly the above-mentioned three ingredients. However, the constitutional arrangement, the electoral system, party system are strongly influenced by the presence of the national minorities or national groups. The main issue is to accommodate these groups and to give them the possibility of participation in a state decision-making process. Several adjustments were made, but the empirical cases show how difficult is to find the suitable arrangement for multinational democracies. Consociational and federal arrangement were found to be most matching systems for deeply divided societies. The theoretical part of the present work will be followed by the exam of two empirical cases, Belgium and Spain.