It would seem, then, that in order to have a true race problem the races must mingle in considerable numbers in the same political system. And in that case the ruling factor is not the precise amount of strictly racial difference, as distinct from social, but the actual attitude of the groups toward each other. If this is such as to keep them separate and perhaps hostile, it matters little, as regards the social situation, whether it is based on sound ethnology or not. In the United States the immigration of Europeans, even though they be of stocks considerably different from the older inhabitants, as Italians, Slavs and Jews, seems not to create a true race problem, experience indicating that assimilation will take place within a generation or two. On the other hand, the presence of the Negro in large numbers creates a race problem, because assimilation is generally held undesirable, and does not, in fact, take place. Whether the immigration of Orientals in large numbers to our Pacific coast would create an enduring race question is, perhaps, undetermined, but experience indicates that it would. Permanent race groups in the same social system constitute race caste. It seems to me that this is beyond comparison the most urgent race question with which we have to deal; not only as regards its present aspects, but because it is likely to have a rapid growth. Many countries, including our own, already suffer from it, and the freedom of movement given by modern conditions, together with the persistence of race sentiment, tend to make it almost universal. That is, if the Chinese, for example, can compete successfully with other races in certain industrial functions, there is no reason, apart from legal restriction, why they should not form colonies in every country where those functions are in demand. It is doubtful how far it may be possible to reconcile race caste with the democracy and solidarity which are coming to be the ideals of modern nations. In the Southern United States the caste feeling is not diminishing, and while we hope that it is taking on forms more favorable to the co-operation of the races on a plane of fair play and mutual respect, the issue is somewhat in doubt. Certainly the present condition is not in harmony with democratic ideals, and its defenders can hardly claim more for it than that it makes the best of a difficult situation. Much the same appears to be true of the contact of races in other parts of the world, in South Africa, Australia, India, and even in Eastern Europe.