Although communism is supposed to be a completely world-wide movement, crossing all national barriers and exemplified by the withering away of the state after the dictatorship of the proletariat, (who have more in common with the workers of other countries then with the ruling classes in their own country), not only are many communist frontiers closed, but the political system varies from country to country. National communism is usually characterized by a resistance to foreign communist control and by a certain distinctiveness in national ideology, social institutions, and political strategy. This may cause aggression on the part of the dominant foreign communist power, ideological schism, and cold war. Ideological schism within the country concerned or within neighbouring countries, encouraged by this national distinctiveness, may lead to political purges and severe repression, or to subversive activities.