100 Furthermore, the universal common good requires the encouragement in all nations of every kind of reciprocation between citizens and their intermediate societies. There are many parts of the world where we find groupings of people of more or less different ethnic origin. Nothing must be allowed to prevent reciprocal relations between them. Indeed such a prohibition would flout the very spirit of an age which has done so much to nullify the distances separating peoples. Nor must one overlook the fact that whatever their ethnic background, men possess, besides the special characteristics which distinguish them from other men, other very important elements in common with the rest of mankind. And these can form the basis of their progressive development and self-realization especially in regard to spiritual values. They have, therefore, the right and duty to carry on their lives with others in society.
Source: Pacem in Terris (Vatican.va)